14 files changed, 624 insertions, 13 deletions

diff --git a/packages/main/package.json b/packages/main/package.json
index 4ba6d06..85f9b12 100644
--- a/packages/main/package.json
+++ b/packages/main/package.json
@@ -14,6 +14,7 @@
     "deep-equal": "^2.0.5",
     "electron": "17.1.0",
     "fs-extra": "^10.0.1",
+    "i18next": "^21.6.14",
     "json5": "^2.2.0",
     "lodash-es": "^4.17.21",
     "loglevel": "^1.8.0",
diff --git a/packages/main/src/i18n/I18nStore.ts b/packages/main/src/i18n/I18nStore.ts
new file mode 100644
index 0000000..d833e8a
--- /dev/null
+++ b/packages/main/src/i18n/I18nStore.ts
@@ -0,0 +1,104 @@
+/*
+ * Copyright (C)  2022 Kristóf Marussy <kristof@marussy.com>
+ *
+ * This file is part of Sophie.
+ *
+ * Sophie is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import type { i18n, TFunction } from 'i18next';
+import { IAtom, createAtom } from 'mobx';
+
+import { getLogger } from '../utils/log';
+
+const log = getLogger('I18nStore');
+
+export type UseTranslationResult =
+  | { ready: true; i18n: i18n; t: TFunction }
+  | { ready: false };
+
+export default class I18nStore {
+  private readonly languageChangedAtom: IAtom;
+
+  private readonly namespaceLoadedAtoms: Map<string, IAtom> = new Map();
+
+  private readonly notifyLanguageChange = () =>
+    this.languageChangedAtom.reportObserved();
+
+  constructor(private readonly i18next: i18n) {
+    this.languageChangedAtom = createAtom(
+      'i18next',
+      () => i18next.on('languageChanged', this.notifyLanguageChange),
+      () => i18next.off('languageChanged', this.notifyLanguageChange),
+    );
+  }
+
+  useTranslation(ns?: string): UseTranslationResult {
+    const observed = this.languageChangedAtom.reportObserved();
+    const namespaceToLoad =
+      ns ?? this.i18next.options.defaultNS ?? 'translation';
+    if (
+      this.i18next.isInitialized &&
+      this.i18next.hasLoadedNamespace(namespaceToLoad)
+    ) {
+      return {
+        ready: true,
+        i18n: this.i18next,
+        // eslint-disable-next-line unicorn/no-null -- `i18next` API requires `null`.
+        t: this.i18next.getFixedT(null, namespaceToLoad),
+      };
+    }
+    if (observed) {
+      this.loadNamespace(namespaceToLoad);
+    }
+    return { ready: false };
+  }
+
+  private loadNamespace(ns: string): void {
+    const existingAtom = this.namespaceLoadedAtoms.get(ns);
+    if (existingAtom !== undefined) {
+      existingAtom.reportObserved();
+      return;
+    }
+    const atom = createAtom(`i18next-${ns}`);
+    this.namespaceLoadedAtoms.set(ns, atom);
+    atom.reportObserved();
+
+    const loaded = () => {
+      this.namespaceLoadedAtoms.delete(ns);
+      atom.reportChanged();
+    };
+
+    const loadAsync = async () => {
+      await this.i18next.loadNamespaces([ns]);
+      if (this.i18next.isInitialized) {
+        setImmediate(loaded);
+        return;
+      }
+      const initialized = () => {
+        setImmediate(() => {
+          this.i18next.off('initialized', initialized);
+          loaded();
+        });
+      };
+      this.i18next.on('initialized', initialized);
+    };
+
+    loadAsync().catch((error) => {
+      log.error('Failed to load translations for namespace', ns, error);
+      setImmediate(loaded);
+    });
+  }
+}
diff --git a/packages/main/src/i18n/LocalizationRepository.ts b/packages/main/src/i18n/LocalizationRepository.ts
new file mode 100644
index 0000000..041449d
--- /dev/null
+++ b/packages/main/src/i18n/LocalizationRepository.ts
@@ -0,0 +1,39 @@
+/*
+ * Copyright (C)  2022 Kristóf Marussy <kristof@marussy.com>
+ *
+ * This file is part of Sophie.
+ *
+ * Sophie is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import type { ResourceKey } from 'i18next';
+
+export default interface LocatlizationRepository {
+  getResourceContents(
+    language: string,
+    namespace: string,
+  ): Promise<ResourceKey>;
+
+  getMissingResourceContents(
+    language: string,
+    namespace: string,
+  ): Promise<ResourceKey>;
+
+  setMissingResourceContents(
+    language: string,
+    namespace: string,
+    data: ResourceKey,
+  ): Promise<void>;
+}
diff --git a/packages/main/src/i18n/RepositoryBasedI18nBackend.ts b/packages/main/src/i18n/RepositoryBasedI18nBackend.ts
new file mode 100644
index 0000000..4d87ce9
--- /dev/null
+++ b/packages/main/src/i18n/RepositoryBasedI18nBackend.ts
@@ -0,0 +1,224 @@
+/*
+ * Copyright (C)  2022 Kristóf Marussy <kristof@marussy.com>
+ *
+ * This file is part of Sophie.
+ *
+ * Sophie is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import type {
+  BackendModule,
+  InitOptions,
+  ReadCallback,
+  Services,
+} from 'i18next';
+import { debounce } from 'lodash-es';
+import ms from 'ms';
+
+import { getLogger } from '../utils/log';
+
+import type LocatlizationRepository from './LocalizationRepository';
+
+const MISSING_ENTRIES_DEBOUNCE_TIME = ms('1s');
+
+const log = getLogger('RepositoryBasedI18nBackend');
+
+/**
+ * I18next backend for loading translations from a file.
+ *
+ * Loosely based on [i18next-fs-backend](https://github.com/i18next/i18next-fs-backend),
+ * but we shrink bundle size by omitting JSON5 or YAML translation handling.
+ * Direct file IO is replaced by the `LocalizationRepository`,
+ * which handles platform-specific concerns.
+ */
+export default class RepositoryBasedI18nBackend
+  implements BackendModule<unknown>
+{
+  type = 'backend' as const;
+
+  private writeQueue: Map<string, Map<string, Map<string, string>>> = new Map();
+
+  private keySeparator: string | false = '.';
+
+  private readonly flushWriteQueueImmediately = () => {
+    const savedWriteQueue = this.writeQueue;
+    this.writeQueue = new Map();
+    savedWriteQueue.forEach((languagesMap, namespace) => {
+      languagesMap.forEach((keysMap, language) => {
+        this.flushChanges(language, namespace, keysMap).catch((error) => {
+          log.error(
+            'Cannot write missing',
+            language,
+            'translations for namespace',
+            namespace,
+            error,
+          );
+        });
+      });
+    });
+  };
+
+  private readonly flushWriteQueue = debounce(
+    this.flushWriteQueueImmediately,
+    MISSING_ENTRIES_DEBOUNCE_TIME,
+  );
+
+  constructor(
+    private readonly repository: LocatlizationRepository,
+    private readonly devMode = false,
+  ) {}
+
+  init(
+    _services: Services,
+    _backendOptions: unknown,
+    { keySeparator }: InitOptions,
+  ) {
+    if (keySeparator !== undefined) {
+      this.keySeparator = keySeparator;
+    }
+  }
+
+  read(language: string, namespace: string, callback: ReadCallback): void {
+    const readAsync = async () => {
+      const translations = await this.repository.getResourceContents(
+        language,
+        namespace,
+      );
+      // eslint-disable-next-line unicorn/no-null -- `i18next` API requires `null`.
+      setImmediate(() => callback(null, translations));
+    };
+
+    readAsync().catch((error) => {
+      log.error(
+        'Error while loading',
+        language,
+        'translations for namespace',
+        namespace,
+        error,
+      );
+      const callbackError =
+        error instanceof Error
+          ? error
+          : new Error(`Unknown error: ${JSON.stringify(error)}`);
+      /*
+        eslint-disable-next-line promise/no-callback-in-promise, unicorn/no-null --
+        Converting from promise based API to a callback. `i18next` API requires `null`.
+      */
+      setImmediate(() => callback(callbackError, null));
+    });
+  }
+
+  create(
+    languages: string[],
+    namespace: string,
+    key: string,
+    fallbackValue: string,
+  ): void {
+    if (!this.devMode) {
+      throw new Error(
+        'Refusing to write missing translations in production mode',
+      );
+    }
+    let languagesMapOrUndefined = this.writeQueue.get(namespace);
+    if (languagesMapOrUndefined === undefined) {
+      languagesMapOrUndefined = new Map();
+      this.writeQueue.set(namespace, languagesMapOrUndefined);
+    }
+    const languagesMap = languagesMapOrUndefined;
+    languages.forEach((language) => {
+      let keysMap = languagesMap.get(language);
+      if (keysMap === undefined) {
+        keysMap = new Map();
+        languagesMap.set(language, keysMap);
+      }
+      keysMap.set(key, fallbackValue);
+    });
+    this.flushWriteQueue();
+  }
+
+  /**
+   * Flushes new translations to the missing translations file.
+   *
+   * Will always fails if `devMode` is `false`.
+   * If no changes are made to the translations, the file won't be rewritten.
+   *
+   * @param language The language to add translations for.
+   * @param namespace The namespace to add translations for.
+   * @param entries The translations to add.
+   * @returns A promise that resolves when changes were flushed successfully.
+   */
+  private async flushChanges(
+    language: string,
+    namespace: string,
+    entries: Map<string, string>,
+  ): Promise<void> {
+    if (!this.devMode) {
+      throw new Error(
+        'Refusing to write missing translations in production mode',
+      );
+    }
+    const resourceContents = await this.repository.getMissingResourceContents(
+      language,
+      namespace,
+    );
+    const translations =
+      typeof resourceContents === 'object' ? resourceContents : {};
+    let changed = false;
+    entries.forEach((value, key) => {
+      const splitKey = this.keySeparator ? key.split(this.keySeparator) : [key];
+      let obj = translations;
+      /*
+        eslint-disable @typescript-eslint/no-unsafe-assignment,
+        security/detect-object-injection --
+        We need to modify raw objects, because this is the storage format for i18next.
+        To mitigate the prototype injection security risk,
+        we make sure to only ever run this in development mode.
+      */
+      for (let i = 0; i < splitKey.length - 1; i += 1) {
+        let nextObj = obj[splitKey[i]];
+        if (typeof nextObj !== 'object') {
+          nextObj = {};
+          obj[splitKey[i]] = nextObj;
+        }
+        obj = nextObj;
+      }
+      const lastKey = splitKey[splitKey.length - 1];
+      if (obj[lastKey] !== value) {
+        obj[lastKey] = value;
+        changed = true;
+      }
+      /*
+        eslint-enable @typescript-eslint/no-unsafe-assignment,
+        security/detect-object-injection
+      */
+    });
+    if (!changed) {
+      return;
+    }
+    await this.repository.setMissingResourceContents(
+      language,
+      namespace,
+      translations,
+    );
+    log.debug(
+      'Wrote',
+      entries.size,
+      'missing',
+      language,
+      'translations for namespace',
+      namespace,
+    );
+  }
+}
diff --git a/packages/main/src/i18n/i18nLog.ts b/packages/main/src/i18n/i18nLog.ts
new file mode 100644
index 0000000..33a8c4e
--- /dev/null
+++ b/packages/main/src/i18n/i18nLog.ts
@@ -0,0 +1,41 @@
+/*
+ * Copyright (C)  2022 Kristóf Marussy <kristof@marussy.com>
+ *
+ * This file is part of Sophie.
+ *
+ * Sophie is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import type { LoggerModule } from 'i18next';
+
+import { getLogger } from '../utils/log';
+
+const log = getLogger('i18nLog');
+
+/*
+  eslint-disable-next-line @typescript-eslint/unbound-method --
+  loglevel log methods don't rely on `this`, so this is safe,
+  and also keeps stacktraces smaller.
+*/
+const { debug, warn, error } = log;
+
+const i18nLog: LoggerModule = {
+  type: 'logger',
+  log: debug,
+  warn,
+  error,
+};
+
+export default i18nLog;
diff --git a/packages/main/src/i18n/impl/LocaltizationFiles.ts b/packages/main/src/i18n/impl/LocaltizationFiles.ts
new file mode 100644
index 0000000..73a769e
--- /dev/null
+++ b/packages/main/src/i18n/impl/LocaltizationFiles.ts
@@ -0,0 +1,93 @@
+/*
+ * Copyright (C)  2022 Kristóf Marussy <kristof@marussy.com>
+ *
+ * This file is part of Sophie.
+ *
+ * Sophie is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import { readFile, writeFile } from 'node:fs/promises';
+
+import type { ResourceKey } from 'i18next';
+
+import type Resources from '../../infrastructure/resources/Resources';
+import isErrno from '../../utils/isErrno';
+import { getLogger } from '../../utils/log';
+import type LocatlizationRepository from '../LocalizationRepository';
+
+const log = getLogger('LocalizationFiles');
+
+export default class LocalizationFiles implements LocatlizationRepository {
+  constructor(private readonly resources: Resources) {}
+
+  async getResourceContents(
+    language: string,
+    namespace: string,
+  ): Promise<ResourceKey> {
+    const fileName = this.resources.getLocalizationPath(
+      language,
+      `${namespace}.json`,
+    );
+    const contents = await readFile(fileName, 'utf8');
+    log.info('Read localization file', fileName);
+    // The contents of the file should come from a signed archive during production,
+    // so we don't need to (and can't) validate them.
+    return JSON.parse(contents) as ResourceKey;
+  }
+
+  private getMissingLocalizationPath(
+    language: string,
+    namespace: string,
+  ): string {
+    return this.resources.getLocalizationPath(
+      language,
+      `${namespace}.missing.json`,
+    );
+  }
+
+  async getMissingResourceContents(
+    language: string,
+    namespace: string,
+  ): Promise<ResourceKey> {
+    const fileName = this.getMissingLocalizationPath(language, namespace);
+    try {
+      const contents = await readFile(fileName, 'utf8');
+      // The contents of the file are only used during development,
+      // so we don't need to (and can't) validate them.
+      return JSON.parse(contents) as ResourceKey;
+    } catch (error) {
+      if (isErrno(error, 'ENOENT')) {
+        log.debug(
+          'No missing translations file',
+          language,
+          'for namespace',
+          namespace,
+        );
+        return {};
+      }
+      throw error;
+    }
+  }
+
+  setMissingResourceContents(
+    language: string,
+    namespace: string,
+    data: ResourceKey,
+  ): Promise<void> {
+    const fileName = this.getMissingLocalizationPath(language, namespace);
+    const contents = JSON.stringify(data, undefined, 2);
+    return writeFile(fileName, contents, 'utf8');
+  }
+}
diff --git a/packages/main/src/i18n/loadLocalization.ts b/packages/main/src/i18n/loadLocalization.ts
new file mode 100644
index 0000000..1408a30
--- /dev/null
+++ b/packages/main/src/i18n/loadLocalization.ts
@@ -0,0 +1,50 @@
+/*
+ * Copyright (C)  2022 Kristóf Marussy <kristof@marussy.com>
+ *
+ * This file is part of Sophie.
+ *
+ * Sophie is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import i18next from 'i18next';
+
+import type Resources from '../infrastructure/resources/Resources';
+import type MainStore from '../stores/MainStore';
+
+import I18nStore from './I18nStore';
+import RepositoryBasedI18nBackend from './RepositoryBasedI18nBackend';
+import i18nLog from './i18nLog';
+import LocalizationFiles from './impl/LocaltizationFiles';
+
+export default async function loadLocalization(
+  store: MainStore,
+  resources: Resources,
+  devMode: boolean,
+): Promise<void> {
+  const repository = new LocalizationFiles(resources);
+  const backend = new RepositoryBasedI18nBackend(repository, devMode);
+  const i18n = i18next
+    .createInstance({
+      lng: 'en',
+      fallbackLng: ['en'],
+      debug: devMode,
+      saveMissing: devMode,
+    })
+    .use(backend)
+    .use(i18nLog);
+  await i18n.init();
+  const i18nStore = new I18nStore(i18n);
+  store.setI18n(i18nStore);
+}
diff --git a/packages/main/src/infrastructure/config/impl/ConfigFile.ts b/packages/main/src/infrastructure/config/impl/ConfigFile.ts
index e8237b4..4ad0fcc 100644
--- a/packages/main/src/infrastructure/config/impl/ConfigFile.ts
+++ b/packages/main/src/infrastructure/config/impl/ConfigFile.ts
@@ -27,6 +27,7 @@ import { throttle } from 'lodash-es';
 
 import type Config from '../../../stores/config/Config';
 import type Disposer from '../../../utils/Disposer';
+import isErrno from '../../../utils/isErrno';
 import { getLogger } from '../../../utils/log';
 import type ConfigRepository from '../ConfigRepository';
 import type { ReadConfigResult } from '../ConfigRepository';
@@ -55,7 +56,7 @@ export default class ConfigFile implements ConfigRepository {
     try {
       configStr = await readFile(this.#configFilePath, 'utf8');
     } catch (error) {
-      if ((error as NodeJS.ErrnoException).code === 'ENOENT') {
+      if (isErrno(error, 'ENOENT')) {
         log.debug('Config file', this.#configFilePath, 'was not found');
         return { found: false };
       }
@@ -94,7 +95,7 @@ export default class ConfigFile implements ConfigRepository {
         mtime = stats.mtime;
         log.trace('Config file last modified at', mtime);
       } catch (error) {
-        if ((error as NodeJS.ErrnoException).code === 'ENOENT') {
+        if (isErrno(error, 'ENOENT')) {
           log.debug(
             'Config file',
             this.#configFilePath,
diff --git a/packages/main/src/infrastructure/electron/impl/setApplicationMenu.ts b/packages/main/src/infrastructure/electron/impl/setApplicationMenu.ts
index 5166719..49bfbfd 100644
--- a/packages/main/src/infrastructure/electron/impl/setApplicationMenu.ts
+++ b/packages/main/src/infrastructure/electron/impl/setApplicationMenu.ts
@@ -30,6 +30,12 @@ export default function setApplicationMenu(
   isMac: boolean,
 ): void {
   const dispose = autorun(() => {
+    const translation = store.useTranslation();
+    if (!translation.ready) {
+      return;
+    }
+    const { t } = translation;
+
     const { settings, shared, visibleService } = store;
     const { showLocationBar, selectedService } = settings;
     const { canSwitchServices, services } = shared;
@@ -42,7 +48,7 @@ export default function setApplicationMenu(
         role: 'viewMenu',
         submenu: [
           {
-            label: 'Show Location Bar',
+            label: t<string>('menu.view.showLocationBar'),
             accelerator: 'CommandOrControl+Shift+L',
             type: 'checkbox',
             checked: showLocationBar,
@@ -52,7 +58,7 @@ export default function setApplicationMenu(
           },
           { type: 'separator' },
           {
-            label: 'Reload',
+            label: t<string>('menu.view.reload'),
             accelerator: 'CommandOrControl+R',
             enabled: selectedService !== undefined,
             click() {
@@ -60,7 +66,7 @@ export default function setApplicationMenu(
             },
           },
           {
-            label: 'Force Reload',
+            label: t<string>('menu.view.forceReload'),
             accelerator: 'CommandOrControl+Shift+R',
             enabled: selectedService !== undefined,
             click() {
@@ -68,7 +74,7 @@ export default function setApplicationMenu(
             },
           },
           {
-            label: 'Toggle Developer Tools',
+            label: t<string>('menu.view.toggleDeveloperTools'),
             accelerator: 'CommandOrControl+Shift+I',
             enabled: visibleService !== undefined,
             click() {
@@ -80,12 +86,15 @@ export default function setApplicationMenu(
             ? ([
                 {
                   role: 'forceReload',
-                  label: 'Reload Sophie',
+                  label: t<string>('menu.view.reloadSophie'),
                   accelerator: 'CommandOrControl+Shift+Alt+R',
                 },
                 {
                   role: 'toggleDevTools',
-                  label: 'Toggle Sophie Developer Tools',
+                  label: t<string>(
+                    'menu.view.toggleSophieDeveloperTools',
+                    'Toggle Sophie Developer Tools',
+                  ),
                   accelerator: 'CommandOrControl+Shift+Alt+I',
                 },
                 { type: 'separator' },
@@ -95,10 +104,10 @@ export default function setApplicationMenu(
         ],
       },
       {
-        label: 'Services',
+        label: t<string>('menu.servicesMenu'),
         submenu: [
           {
-            label: 'Next Service',
+            label: t<string>('menu.services.nextService'),
             accelerator: 'CommandOrControl+Tab',
             enabled: canSwitchServices,
             click() {
@@ -106,7 +115,7 @@ export default function setApplicationMenu(
             },
           },
           {
-            label: 'Previous Service',
+            label: t<string>('menu.services.previousService'),
             accelerator: 'CommandOrControl+Shift+Tab',
             enabled: canSwitchServices,
             click() {
@@ -140,7 +149,7 @@ export default function setApplicationMenu(
         role: 'help',
         submenu: [
           {
-            label: 'Gitlab',
+            label: t<string>('menu.help.gitlab'),
             click() {
               store.openWebpageInBrowser();
             },
diff --git a/packages/main/src/infrastructure/resources/Resources.ts b/packages/main/src/infrastructure/resources/Resources.ts
index 269c838..0e90c6b 100644
--- a/packages/main/src/infrastructure/resources/Resources.ts
+++ b/packages/main/src/infrastructure/resources/Resources.ts
@@ -21,6 +21,8 @@
 export default interface Resources {
   getPath(packageName: string, relativePathInPackage: string): string;
 
+  getLocalizationPath(language: string, fileName: string): string;
+
   getFileURL(packageName: string, relativePathInPackage: string): string;
 
   getRendererURL(relativePathInRendererPackage: string): string;
diff --git a/packages/main/src/infrastructure/resources/impl/getDistResources.ts b/packages/main/src/infrastructure/resources/impl/getDistResources.ts
index f3c3f7b..3c1ffb3 100644
--- a/packages/main/src/infrastructure/resources/impl/getDistResources.ts
+++ b/packages/main/src/infrastructure/resources/impl/getDistResources.ts
@@ -33,6 +33,7 @@ export default function getDistResources(
   devServerURL = import.meta.env?.VITE_DEV_SERVER_URL,
 ): Resources {
   const packagesRoot = path.join(thisDir, '..', '..');
+  const localizationRoot = path.join(packagesRoot, '..', 'locales');
 
   function getPath(packageName: string, relativePathInPackage: string): string {
     return path.join(packagesRoot, packageName, 'dist', relativePathInPackage);
@@ -48,6 +49,9 @@ export default function getDistResources(
 
   return {
     getPath,
+    getLocalizationPath(language, fileName) {
+      return path.join(localizationRoot, language, fileName);
+    },
     getFileURL,
     getRendererURL:
       devMode && devServerURL !== undefined
diff --git a/packages/main/src/initReactions.ts b/packages/main/src/initReactions.ts
index 9c49fc5..cdff551 100644
--- a/packages/main/src/initReactions.ts
+++ b/packages/main/src/initReactions.ts
@@ -20,6 +20,7 @@
 
 import { app, session } from 'electron';
 
+import loadLocalization from './i18n/loadLocalization';
 import ConfigFile from './infrastructure/config/impl/ConfigFile';
 import UserAgents from './infrastructure/electron/UserAgents';
 import ElectronViewFactory from './infrastructure/electron/impl/ElectronViewFactory';
@@ -52,7 +53,11 @@ export default async function initReactions(
   }
   const userAgents = new UserAgents(app.userAgentFallback);
   app.userAgentFallback = userAgents.fallbackUserAgent(devMode);
-  setApplicationMenu(store, devMode, isMac);
+  const localizeInterface = async () => {
+    await loadLocalization(store, resources, devMode);
+    setApplicationMenu(store, devMode, isMac);
+  };
+  const localization = localizeInterface();
   const viewFactory = new ElectronViewFactory(userAgents, resources, devMode);
   const [mainWindow] = await Promise.all([
     viewFactory.createMainWindow(store),
@@ -60,6 +65,7 @@ export default async function initReactions(
   ]);
   store.setMainWindow(mainWindow);
   loadServices(store, viewFactory);
+  await localization;
   return () => {
     disposeNativeThemeController();
     disposeConfigController();
diff --git a/packages/main/src/stores/MainStore.ts b/packages/main/src/stores/MainStore.ts
index 86fadcb..873f998 100644
--- a/packages/main/src/stores/MainStore.ts
+++ b/packages/main/src/stores/MainStore.ts
@@ -21,6 +21,8 @@
 import type { Action, BrowserViewBounds } from '@sophie/shared';
 import { applySnapshot, Instance, types } from 'mobx-state-tree';
 
+import type I18nStore from '../i18n/I18nStore';
+import type { UseTranslationResult } from '../i18n/I18nStore';
 import type { MainWindow } from '../infrastructure/electron/types';
 import { getLogger } from '../utils/log';
 
@@ -44,6 +46,7 @@ const MainStore = types
       {},
     ),
     shared: types.optional(SharedStore, {}),
+    i18n: types.frozen<I18nStore | undefined>(),
   })
   .views((self) => ({
     get settings(): GlobalSettings {
@@ -61,6 +64,9 @@ const MainStore = types
         ? selectedService
         : undefined;
     },
+    useTranslation(ns?: string): UseTranslationResult {
+      return self.i18n?.useTranslation(ns) ?? { ready: false };
+    },
   }))
   .volatile(
     (): {
@@ -124,6 +130,9 @@ const MainStore = types
     beforeDestroy(): void {
       self.mainWindow?.dispose();
     },
+    setI18n(i18n: I18nStore): void {
+      self.i18n = i18n;
+    },
   }));
 
 /*
diff --git a/packages/main/src/utils/isErrno.ts b/packages/main/src/utils/isErrno.ts
new file mode 100644
index 0000000..8adbc33
--- /dev/null
+++ b/packages/main/src/utils/isErrno.ts
@@ -0,0 +1,28 @@
+/*
+ * Copyright (C)  2021-2022 Kristóf Marussy <kristof@marussy.com>
+ *
+ * This file is part of Sophie.
+ *
+ * Sophie is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+export default function isErrno(error: unknown, code: string): boolean {
+  return (
+    typeof error === 'object' &&
+    error !== null &&
+    'code' in error &&
+    (error as NodeJS.ErrnoException).code === code
+  );
+}