diff --git a/src/extensions/locales-defaults/index.ts b/src/extensions/locales-defaults/index.ts
index dd6b592c7..4d46cc1e8 100644
--- a/src/extensions/locales-defaults/index.ts
+++ b/src/extensions/locales-defaults/index.ts
@@ -2,8 +2,7 @@ import { IExtension, IContributeType } from 'mo/model/extension';
 
 const zhCN = require('./locales/zh-CN.json');
 const en = require('./locales/en.json');
-const getLocalesList = () => [zhCN, en];
-const locales = getLocalesList() || [];
+const locales = [zhCN, en];
 
 export const ExtendsLocales: IExtension = {
     id: 'ExtendsLocales',
@@ -15,5 +14,5 @@ export const ExtendsLocales: IExtension = {
     dispose() {},
 };
 export const BuiltInLocales = locales;
-export const BuiltInDefault = locales.find((item) => item.id === en.id);
 export const BuiltInId = en.id;
+export const BuiltInDefault = locales.find((item) => item.id === BuiltInId);
diff --git a/src/i18n/__tests__/localeService.test.ts b/src/i18n/__tests__/localeService.test.ts
new file mode 100644
index 000000000..b5f5260a5
--- /dev/null
+++ b/src/i18n/__tests__/localeService.test.ts
@@ -0,0 +1,173 @@
+import 'reflect-metadata';
+import { container } from 'tsyringe';
+import { LocaleService } from '..';
+import { BuiltInLocales, BuiltInDefault, ILocale } from '../localization';
+
+describe('The Locale Service', () => {
+    const TestLocale = {
+        id: 'test',
+        source: new Map(),
+        name: 'test',
+    };
+
+    afterEach(() => {
+        localStorage.clear();
+    });
+
+    test('Instance the LocaleService by IOC', () => {
+        const localeService = container.resolve(LocaleService);
+        expect(localeService).not.toBeUndefined();
+    });
+
+    test('Reset the LocaleService', () => {
+        const localeService = new LocaleService();
+        expect(localeService.getCurrentLocale()!.id).toBe(BuiltInDefault.id);
+        localeService.reset();
+        expect(localeService.getCurrentLocale()).toBeUndefined();
+    });
+
+    test('Get default Locale', () => {
+        const localeService = new LocaleService();
+        const defaultLocale = localeService.getDefaultLocale();
+        expect(defaultLocale).toEqual(BuiltInDefault);
+    });
+
+    test('Get default Locales', () => {
+        const localeService = new LocaleService();
+        const defaultLocale = localeService.getDefaultLocales();
+        expect(defaultLocale).toEqual(BuiltInLocales);
+    });
+
+    test('The size of Built-in Locales should be 2', () => {
+        const localeService = new LocaleService();
+        const locales = localeService.getLocales();
+        expect(locales.length).toBe(2);
+    });
+
+    test('Initialize the locales', () => {
+        const localeService = new LocaleService();
+        localeService.initialize([TestLocale]);
+        expect(localeService.getCurrentLocale()!.id).toEqual(
+            localeService.getDefaultLocale().id
+        );
+        expect(localeService.getLocales().length).toBe(3);
+        localeService.initialize([], 'test');
+        expect(localeService.getCurrentLocale()!.id).toEqual(BuiltInDefault.id);
+        // Clear the cached locale value
+        localStorage.clear();
+        localeService.initialize([], 'test');
+        expect(localeService.getCurrentLocale()!.id).toEqual('test');
+        localeService.initialize([]);
+        // Get from the localStorage cache
+        expect(localeService.getCurrentLocale()!.id).toEqual('test');
+    });
+
+    test('Get/Set current locale', () => {
+        const localeService = new LocaleService();
+        (localeService as any)._current = undefined;
+        expect(localeService.getCurrentLocale()).toBeUndefined();
+        localeService.addLocales([TestLocale]);
+        localeService.setCurrentLocale(TestLocale.id);
+        expect(localeService.getCurrentLocale()!.id).toEqual(TestLocale.id);
+
+        expect(localeService.setCurrentLocale('unknown')).toEqual(false);
+    });
+
+    test('Add locales', () => {
+        const localeService = new LocaleService();
+        expect(localeService.getLocales().length).toBe(2);
+        localeService.addLocales([TestLocale]);
+        expect(localeService.getLocales().length).toBe(3);
+        localeService.addLocales([]);
+        expect(localeService.getLocales().length).toBe(3);
+        // Add an existed locale
+        localeService.addLocales([TestLocale]);
+        expect(localeService.getLocales().length).toBe(3);
+    });
+
+    test('Add an locale inherit the en', () => {
+        const localeService = new LocaleService();
+        expect(TestLocale.source.size).toBe(0);
+        (TestLocale as ILocale).inherit = 'en';
+        localeService.addLocales([TestLocale]);
+        expect(localeService.getLocale(TestLocale.id)?.source.size).not.toBe(0);
+
+        // Inherit an not exist locale
+        localeService.removeLocale(TestLocale.id);
+        (TestLocale as ILocale).inherit = 'unknown';
+        localeService.addLocales([TestLocale]);
+        expect(localeService.getLocale(TestLocale.id)?.source.size).toBe(0);
+    });
+
+    test('Get a specific locale', () => {
+        const localeService = new LocaleService();
+        localeService.addLocales([TestLocale]);
+        expect(localeService.getLocale(TestLocale.id)).not.toBeNull();
+        expect(localeService.getLocale(TestLocale.id)?.id).toEqual(
+            TestLocale.id
+        );
+    });
+
+    test('Remove a locale', () => {
+        const localeService = new LocaleService();
+        localeService.addLocales([TestLocale]);
+        expect(localeService.getLocale(TestLocale.id)?.id).toEqual(
+            TestLocale.id
+        );
+        localeService.removeLocale(TestLocale.id);
+        expect(localeService.getLocale(TestLocale.id)).toBeUndefined();
+        localeService.addLocales([TestLocale]);
+        localeService.setCurrentLocale(TestLocale.id);
+
+        //Remove the current locale
+        expect(localeService.getCurrentLocale()!.id).toEqual(TestLocale.id);
+        localeService.removeLocale(TestLocale.id);
+        expect(localeService.getCurrentLocale()!.id).toEqual(
+            localeService.getDefaultLocale().id
+        );
+
+        // Remove an undefined
+        expect(localeService.removeLocale(TestLocale.id));
+    });
+
+    test('Listen to the current locale change event', () => {
+        const target = 'zh-CN';
+        const localeService = new LocaleService();
+        const fn = jest.fn();
+        localeService.onChange(fn);
+        localeService.setCurrentLocale(target);
+        expect(fn).toBeCalledTimes(1);
+        expect(localeService.getCurrentLocale()!.id).toEqual(target);
+    });
+
+    test('Localize the source key', () => {
+        const localeService = new LocaleService();
+        let res = localeService.localize('test');
+        expect(res).toEqual('');
+
+        res = localeService.localize('test', 'default');
+        expect(res).toEqual('default');
+
+        res = localeService.localize('molecule.welcome');
+        expect(res).toEqual('Welcome to Molecule');
+
+        res = localeService.localize('molecule.welcome', 'default');
+        expect(res).toEqual('Welcome to Molecule');
+
+        const map = new Map();
+        map.set('test.id', 'hello ${i}');
+        const mockData = {
+            id: 'mock',
+            name: 'mock',
+            source: map,
+        };
+        localeService.addLocales([mockData]);
+        localeService.setCurrentLocale(mockData.id);
+        res = localeService.localize('test.id', '', 'world');
+        expect(res).toEqual('hello world');
+
+        (localeService as any)._current = null;
+        res = localeService.localize('molecule.welcome', 'default');
+        expect(res).toEqual('default');
+    });
+});
diff --git a/src/i18n/localeService.ts b/src/i18n/localeService.ts
index 99c6fc39b..d2204702a 100644
--- a/src/i18n/localeService.ts
+++ b/src/i18n/localeService.ts
@@ -4,7 +4,6 @@ import {
     LocalizationEvent,
     BuiltInLocales,
     BuiltInDefault,
-    BuiltInId,
 } from 'mo/i18n/localization';
 
 import { Component } from 'mo/react';
@@ -99,7 +98,7 @@ export class LocaleService extends Component implements ILocaleService {
         /**
          * TODO: It will then be removed accordingly
          */
-        this.initialize(BuiltInLocales, BuiltInId);
+        this.initialize(BuiltInLocales);
     }
 
     public reset(): void {