diff --git a/packages/core/src/routes/custom-phrase.ts b/packages/core/src/routes/custom-phrase.ts
index be56cf943..d1c4dcc72 100644
--- a/packages/core/src/routes/custom-phrase.ts
+++ b/packages/core/src/routes/custom-phrase.ts
@@ -34,6 +34,7 @@ export default function customPhraseRoutes<T extends AuthedRouter>(
     '/custom-phrases',
     koaGuard({
       response: CustomPhrases.guard.array(),
+      status: [200],
     }),
     async (ctx, next) => {
       ctx.body = await findAllCustomPhrases();
@@ -47,6 +48,7 @@ export default function customPhraseRoutes<T extends AuthedRouter>(
     koaGuard({
       params: object({ languageTag: languageTagGuard }),
       response: CustomPhrases.guard,
+      status: [200],
     }),
     async (ctx, next) => {
       const {
@@ -65,6 +67,7 @@ export default function customPhraseRoutes<T extends AuthedRouter>(
       params: object({ languageTag: languageTagGuard }),
       body: translationGuard,
       response: CustomPhrases.guard,
+      status: [200],
     }),
     async (ctx, next) => {
       const {
@@ -89,6 +92,7 @@ export default function customPhraseRoutes<T extends AuthedRouter>(
     '/custom-phrases/:languageTag',
     koaGuard({
       params: object({ languageTag: languageTagGuard }),
+      status: [204],
     }),
     async (ctx, next) => {
       const {
diff --git a/packages/integration-tests/package.json b/packages/integration-tests/package.json
index c626d9e0e..c7cdbf0f7 100644
--- a/packages/integration-tests/package.json
+++ b/packages/integration-tests/package.json
@@ -23,6 +23,7 @@
   "devDependencies": {
     "@jest/types": "^29.1.2",
     "@logto/connector-kit": "workspace:^1.1.0",
+    "@logto/language-kit": "workspace:^1.0.0",
     "@logto/js": "^2.0.1",
     "@logto/node": "^2.0.0",
     "@logto/schemas": "workspace:^1.1.0",
diff --git a/packages/integration-tests/src/api/custom-phrase.ts b/packages/integration-tests/src/api/custom-phrase.ts
new file mode 100644
index 000000000..6e2beb264
--- /dev/null
+++ b/packages/integration-tests/src/api/custom-phrase.ts
@@ -0,0 +1,17 @@
+import type { CustomPhrase, Translation } from '@logto/schemas';
+
+import { authedAdminApi } from './api.js';
+
+export const listCustomPhrases = async () =>
+  authedAdminApi.get('custom-phrases').json<CustomPhrase[]>();
+
+export const getCustomPhrase = async (languageTag: string) =>
+  authedAdminApi.get(`custom-phrases/${languageTag}`).json<CustomPhrase>();
+
+export const createOrUpdateCustomPhrase = async (languageTag: string, translation: Translation) =>
+  authedAdminApi
+    .put({ url: `custom-phrases/${languageTag}`, json: translation })
+    .json<CustomPhrase>();
+
+export const deleteCustomPhrase = async (languageTag: string) =>
+  authedAdminApi.delete(`custom-phrases/${languageTag}`).json();
diff --git a/packages/integration-tests/src/tests/api/custom-phrase.test.ts b/packages/integration-tests/src/tests/api/custom-phrase.test.ts
new file mode 100644
index 000000000..133605f7b
--- /dev/null
+++ b/packages/integration-tests/src/tests/api/custom-phrase.test.ts
@@ -0,0 +1,96 @@
+import { HTTPError } from 'got';
+
+import {
+  listCustomPhrases,
+  getCustomPhrase,
+  createOrUpdateCustomPhrase,
+  deleteCustomPhrase,
+} from '#src/api/custom-phrase.js';
+
+const mockZhTranslation = {
+  input: {
+    email: '邮箱',
+    password: '密码',
+    username: '用户名',
+    phone_number: '手机号码',
+    confirm_password: '确认密码',
+    search_region_code: '搜索区号',
+  },
+};
+
+const mockZhTranslationUpdated = {
+  ...mockZhTranslation,
+  description: {
+    email: '邮箱',
+    phone_number: '手机号码',
+  },
+};
+
+const mockEnUsTranslation = {
+  input: {
+    email: 'email',
+    password: 'password',
+    username: 'username',
+    phone_number: 'phone_number',
+    confirm_password: 'confirm password',
+    search_region_code: 'search region code',
+  },
+};
+
+describe('custom-phrase flow', () => {
+  it('failed create a non built-in custom phrase with invalid language tag (zh-ZH)', async () => {
+    await expect(createOrUpdateCustomPhrase('zh-ZH', mockZhTranslation)).rejects.toThrow(HTTPError);
+  });
+
+  it('create a non built-in custom phrase (zh)', async () => {
+    await createOrUpdateCustomPhrase('zh', mockZhTranslation);
+    const { translation: zhTranslation } = await getCustomPhrase('zh');
+    expect(zhTranslation).toEqual(mockZhTranslation);
+  });
+
+  it('customize a built-in custom phrase (en-US)', async () => {
+    await createOrUpdateCustomPhrase('en-US', mockEnUsTranslation);
+    const { translation: enUsTranslation } = await getCustomPhrase('en-US');
+    expect(enUsTranslation).toEqual(mockEnUsTranslation);
+  });
+
+  it('update an existing custom phrase', async () => {
+    await createOrUpdateCustomPhrase('zh', mockZhTranslationUpdated);
+    const { translation: zhTranslationNew } = await getCustomPhrase('zh');
+    expect(zhTranslationNew).toEqual(mockZhTranslationUpdated);
+  });
+
+  it('failed to get a custom phrase with invalid language tag (zh-ZH)', async () => {
+    await expect(getCustomPhrase('zh-ZH')).rejects.toThrow(HTTPError);
+  });
+
+  it('failed to get a custom phrase with non-existing record', async () => {
+    await expect(getCustomPhrase('zh-TW')).rejects.toThrow(HTTPError);
+  });
+
+  it('get all custom phrases', async () => {
+    const allCustomPhrases = await listCustomPhrases();
+    expect(allCustomPhrases.find(({ languageTag }) => languageTag === 'zh')?.translation).toEqual(
+      mockZhTranslationUpdated
+    );
+    expect(
+      allCustomPhrases.find(({ languageTag }) => languageTag === 'en-US')?.translation
+    ).toEqual(mockEnUsTranslation);
+  });
+
+  it('failed to delete a custom phrase with invalid language tag (zh-ZH)', async () => {
+    await expect(deleteCustomPhrase('zh-ZH')).rejects.toThrow(HTTPError);
+  });
+
+  it('failed to delete a custom phrase with non-existing record', async () => {
+    await expect(deleteCustomPhrase('zh-TW')).rejects.toThrow(HTTPError);
+  });
+
+  it('delete all custom phrases', async () => {
+    await deleteCustomPhrase('zh');
+    await deleteCustomPhrase('en-US');
+    const allCustomPhrases = await listCustomPhrases();
+    expect(allCustomPhrases.find(({ languageTag }) => languageTag === 'zh')).toBeUndefined();
+    expect(allCustomPhrases.find(({ languageTag }) => languageTag === 'en-US')).toBeUndefined();
+  });
+});
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index d0b63539e..9321d490f 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -3408,6 +3408,9 @@ importers:
       '@logto/js':
         specifier: ^2.0.1
         version: 2.0.1
+      '@logto/language-kit':
+        specifier: workspace:^1.0.0
+        version: link:../toolkit/language-kit
       '@logto/node':
         specifier: ^2.0.0
         version: 2.0.0