fix(core): fall back to base language for API error messages

.changeset/lucky-spoons-itch.md

@@ -0,0 +1,5 @@
+---
+"@logto/core": patch
+---
+
+fix API error messages falling back to English instead of a supported base language for regional language tags

packages/core/src/middleware/koa-i18next.test.ts

@@ -1,31 +1,82 @@
-import { pickDefault, createMockUtils } from '@logto/shared/esm';
+import resources from '@logto/phrases';
 
+import RequestError from '#src/errors/RequestError/index.js';
+import initI18n from '#src/i18n/init.js';
 import { i18next } from '#src/utils/i18n.js';
 import { createContextWithRouteParameters } from '#src/utils/test-utils.js';
 
-const { jest } = import.meta;
-const { mockEsmDefault } = createMockUtils(jest);
-
-const mockLanguage = () => ['zh-cn'];
-mockEsmDefault('#src/i18n/detect-language.js', () => mockLanguage);
+import koaI18next from './koa-i18next.js';
 
-const initI18n = await pickDefault(import('#src/i18n/init.js'));
-const koaI18next = await pickDefault(import('./koa-i18next.js'));
-const cloneInstanceSpy = jest.spyOn(i18next, 'cloneInstance');
+const { jest } = import.meta;
 
 describe('koaI18next', () => {
   const next = jest.fn();
 
-  it('detect language', async () => {
+  beforeAll(async () => {
+    await initI18n();
+  });
+
+  afterEach(() => {
+    jest.clearAllMocks();
+  });
+
+  it.each([
+    ['zh-cn', 'zh-CN'],
+    ['es-MX', 'es'],
+    ['fr-CA', 'fr'],
+    ['pt-BR', 'pt-BR'],
+    ['pt-PT', 'pt-PT'],
+    ['pl', 'pl-PL'],
+    ['en;q=0.5,es-MX;q=0.9', 'es'],
+    ['es-MX;q=0.5,fr;q=0.9', 'fr'],
+    ['xx-XX,fr-CA;q=0.9', 'fr'],
+    ['xx-XX', 'en'],
+    ['*', 'en'],
+    ['', 'en'],
+  ] as const)('localizes API errors for Accept-Language %s to %s', async (language, expected) => {
     const ctx = {
-      ...createContextWithRouteParameters(),
+      ...createContextWithRouteParameters({ headers: { 'accept-language': language } }),
       query: {},
-      i18n: i18next,
-      locale: '',
     };
-    await initI18n();
+
+    await koaI18next()(ctx, next);
+
+    expect(ctx.locale).toEqual(expected);
+    expect(new RequestError('session.not_found').toBody(ctx.i18n)).toMatchObject({
+      code: 'session.not_found',
+      message: resources[expected].errors?.session?.not_found,
+    });
+    expect(next).toHaveBeenCalledTimes(1);
+  });
+
+  it('prioritizes the locale query over Accept-Language', async () => {
+    const ctx = {
+      ...createContextWithRouteParameters({ headers: { 'accept-language': 'es' } }),
+      query: { locale: 'fr-CA' },
+    };
+
     await koaI18next()(ctx, next);
-    expect(ctx.locale).toEqual('zh-CN');
-    expect(cloneInstanceSpy).toBeCalled();
+
+    expect(ctx.locale).toEqual('fr');
+  });
+
+  it('keeps the language scoped to each request', async () => {
+    const spanishContext = {
+      ...createContextWithRouteParameters({ headers: { 'accept-language': 'es-MX' } }),
+      query: {},
+    };
+    const frenchContext = {
+      ...createContextWithRouteParameters({ headers: { 'accept-language': 'fr-CA' } }),
+      query: {},
+    };
+
+    await koaI18next()(spanishContext, next);
+    await koaI18next()(frenchContext, next);
+
+    expect(spanishContext.i18n.language).toEqual('es');
+    expect(frenchContext.i18n.language).toEqual('fr');
+    expect(spanishContext.i18n).not.toBe(frenchContext.i18n);
+    expect(spanishContext.i18n).not.toBe(i18next);
+    expect(i18next.language).toEqual('en');
   });
 });

packages/core/src/middleware/koa-i18next.ts

@@ -1,15 +1,12 @@
+import { findSupportedLanguageTag } from '@logto/language-kit';
+import { builtInLanguages } from '@logto/phrases';
 import type { i18n } from 'i18next';
 import type { MiddlewareType } from 'koa';
 import type { IRouterParamContext } from 'koa-router';
 
 import detectLanguage from '#src/i18n/detect-language.js';
 import { i18next } from '#src/utils/i18n.js';
 
-type LanguageUtils = {
-  formatLanguageCode(code: string): string;
-  isSupportedCode(code: string): boolean;
-};
-
 export type WithI18nContext<ContextT extends IRouterParamContext = IRouterParamContext> =
   ContextT & {
     locale: string;
@@ -23,12 +20,7 @@ export default function koaI18next<
 >(): MiddlewareType<StateT, WithI18nContext<ContextT>, ResponseBodyT> {
   return async (ctx, next) => {
     const languages = detectLanguage(ctx);
-    // Cannot patch type def directly, see https://github.com/microsoft/TypeScript/issues/36146
-    // eslint-disable-next-line no-restricted-syntax
-    const languageUtils = i18next.services.languageUtils as LanguageUtils;
-    const foundLanguage = languages
-      .map((code) => languageUtils.formatLanguageCode(code))
-      .find((code) => languageUtils.isSupportedCode(code));
+    const foundLanguage = findSupportedLanguageTag(languages, builtInLanguages);
 
     // Async requests may change the language, so we need to clone a new instance instead of directly updating
     // the global i18next instance. Keep the i18n context scoped to the request.