Complete client UI i18n migration

Adds client-side i18n support, language settings, translated UI copy, and locale parity coverage.

packages/app/src/hooks/use-settings/index.ts

@@ -2,6 +2,7 @@ import { useCallback } from "react";
 import AsyncStorage from "@react-native-async-storage/async-storage";
 import { useQuery, useQueryClient, type QueryClient } from "@tanstack/react-query";
 import { queryClient as appQueryClient } from "@/query/query-client";
+import type { AppLanguage } from "@/i18n/locales";
 import {
   DEFAULT_DESKTOP_SETTINGS,
   loadDesktopSettings,
@@ -58,6 +59,7 @@ export {
 };
 export type {
   AppSettings,
+  AppLanguage,
   DesktopSettingsBridge,
   KeyValueStorage,
   ReleaseChannel,
@@ -143,6 +145,9 @@ export function useSettings(): UseSettingsReturn {
       if (updates.theme !== undefined) {
         appUpdates.theme = updates.theme;
       }
+      if (updates.language !== undefined) {
+        appUpdates.language = updates.language;
+      }
       if (updates.sendBehavior !== undefined) {
         appUpdates.sendBehavior = updates.sendBehavior;
       }

packages/app/src/hooks/use-settings/storage.test.ts

@@ -47,11 +47,20 @@ describe("loadAppSettingsFromStorage", () => {
     const result = await loadAppSettingsFromStorage(deps);
 
     expect(result).toEqual(DEFAULT_CLIENT_SETTINGS);
+    expect(DEFAULT_CLIENT_SETTINGS.language).toBe("system");
     expect(deps.storage.entries.get(APP_SETTINGS_KEY)).toBe(
       JSON.stringify(DEFAULT_CLIENT_SETTINGS),
     );
   });
 
+  it("defaults language to system when storage is empty", async () => {
+    const deps = makeDeps();
+
+    const result = await loadAppSettingsFromStorage(deps);
+
+    expect(result.language).toBe("system");
+  });
+
   it("loads configured terminal scrollback lines from app settings", async () => {
     const deps = makeDeps({
       storage: createInMemoryKeyValueStorage({
@@ -95,6 +104,30 @@ describe("loadAppSettingsFromStorage", () => {
     });
     expect(deps.storage.entries.get(APP_SETTINGS_KEY)).toBe(JSON.stringify(result));
   });
+
+  it("loads a persisted explicit language", async () => {
+    const deps = makeDeps({
+      storage: createInMemoryKeyValueStorage({
+        [APP_SETTINGS_KEY]: JSON.stringify({ language: "zh-CN" }),
+      }),
+    });
+
+    const result = await loadAppSettingsFromStorage(deps);
+
+    expect(result.language).toBe("zh-CN");
+  });
+
+  it("drops an unknown persisted language back to system", async () => {
+    const deps = makeDeps({
+      storage: createInMemoryKeyValueStorage({
+        [APP_SETTINGS_KEY]: JSON.stringify({ language: "klingon" }),
+      }),
+    });
+
+    const result = await loadAppSettingsFromStorage(deps);
+
+    expect(result.language).toBe("system");
+  });
 });
 
 describe("loadSettingsFromStorage", () => {

packages/app/src/hooks/use-settings/storage.ts

@@ -1,6 +1,7 @@
 import { isSyntaxThemeId, type SyntaxThemeId } from "@getpaseo/highlight";
 import type { QueryClient } from "@tanstack/react-query";
 import type { DesktopSettings } from "@/desktop/settings/desktop-settings";
+import { parseAppLanguage, type AppLanguage } from "@/i18n/locales";
 import { THEME_TO_UNISTYLES, type ThemeName } from "@/styles/theme";
 
 export const APP_SETTINGS_KEY = "@paseo:app-settings";
@@ -26,6 +27,7 @@ export const MAX_FONT_FAMILY_LENGTH = 200;
 
 export interface AppSettings {
   theme: ThemeName | "auto";
+  language: AppLanguage;
   sendBehavior: SendBehavior;
   serviceUrlBehavior: ServiceUrlBehavior;
   terminalScrollbackLines: number;
@@ -43,6 +45,7 @@ export interface Settings extends AppSettings {
 
 export const DEFAULT_CLIENT_SETTINGS: AppSettings = {
   theme: "auto",
+  language: "system",
   sendBehavior: "interrupt",
   serviceUrlBehavior: "ask",
   terminalScrollbackLines: DEFAULT_TERMINAL_SCROLLBACK_LINES,
@@ -149,6 +152,10 @@ function pickAppSettings(stored: Partial<AppSettings>): Partial<AppSettings> {
   if (typeof stored.theme === "string" && VALID_THEMES.has(stored.theme)) {
     result.theme = stored.theme;
   }
+  const language = parseAppLanguage(stored.language);
+  if (language !== null) {
+    result.language = language;
+  }
   if (stored.sendBehavior === "interrupt" || stored.sendBehavior === "queue") {
     result.sendBehavior = stored.sendBehavior;
   }