feat(i18n): add Traditional Chinese localization (#3093)

* Add Traditional Chinese localization

* fix: address zh-TW formatting and token units

- Format `zh-TW.json` with Prettier.
- Use Traditional Chinese `萬` and `億` units for zh-TW token summaries.
- Add usage formatting coverage for Traditional Chinese locale aliases.

---------

Co-authored-by: Jason <farion1231@gmail.com>

tests/components/usageFormat.test.ts

@@ -0,0 +1,17 @@
+import { describe, expect, it } from "vitest";
+import {
+  formatTokensShort,
+  getLocaleFromLanguage,
+} from "@/components/usage/format";
+
+describe("usage format helpers", () => {
+  it("formats Traditional Chinese token units with Traditional characters", () => {
+    expect(formatTokensShort(12_345, "zh-TW")).toBe("1.2 萬");
+    expect(formatTokensShort(123_456_789, "zh-Hant", 2)).toBe("1.23 億");
+  });
+
+  it("resolves Traditional Chinese locale aliases", () => {
+    expect(getLocaleFromLanguage("zh_TW")).toBe("zh-TW");
+    expect(getLocaleFromLanguage("zh-HK")).toBe("zh-TW");
+  });
+});

tests/hooks/useSettingsForm.test.tsx

@@ -81,6 +81,29 @@ describe("useSettingsForm Hook", () => {
     expect(changeLanguageSpy).toHaveBeenCalledWith("ja");
   });
 
+  it("should support traditional chinese language preference aliases", async () => {
+    useSettingsQueryMock.mockReturnValue({
+      data: {
+        showInTray: true,
+        minimizeToTrayOnClose: true,
+        enableClaudePluginIntegration: false,
+        claudeConfigDir: "/Users/demo",
+        codexConfigDir: null,
+        language: "zh-Hant",
+      },
+      isLoading: false,
+    });
+
+    const { result } = renderHook(() => useSettingsForm());
+
+    await waitFor(() => {
+      expect(result.current.settings?.language).toBe("zh-TW");
+    });
+
+    expect(result.current.initialLanguage).toBe("zh-TW");
+    expect(changeLanguageSpy).toHaveBeenCalledWith("zh-TW");
+  });
+
   it("should prioritize reading language from local storage in readPersistedLanguage", () => {
     useSettingsQueryMock.mockReturnValue({
       data: null,