diff --git a/packages/core/src/node/i18n/localization-backend-contribution.ts b/packages/core/src/node/i18n/localization-backend-contribution.ts
index 4ab18bb35e15e..68c0357a50e2c 100644
--- a/packages/core/src/node/i18n/localization-backend-contribution.ts
+++ b/packages/core/src/node/i18n/localization-backend-contribution.ts
@@ -16,12 +16,14 @@
 
 import * as express from 'express';
 import { inject, injectable } from 'inversify';
+import { Deferred } from '../../common/promise-util';
 import { BackendApplicationContribution } from '../backend-application';
 import { LocalizationRegistry } from './localization-contribution';
 import { LocalizationProvider } from './localization-provider';
 
 @injectable()
 export class LocalizationBackendContribution implements BackendApplicationContribution {
+    protected readonly initialized = new Deferred<void>();
 
     @inject(LocalizationRegistry)
     protected readonly localizationRegistry: LocalizationRegistry;
@@ -31,15 +33,20 @@ export class LocalizationBackendContribution implements BackendApplicationContri
 
     async initialize(): Promise<void> {
         await this.localizationRegistry.initialize();
+        this.initialized.resolve();
+    }
+
+    waitForInitialization(): Promise<void> {
+        return this.initialized.promise;
     }
 
     configure(app: express.Application): void {
-        app.get('/i18n/:locale', (req, res) => {
+        app.get('/i18n/:locale', async (req, res) => {
+            await this.waitForInitialization();
             let locale = req.params.locale;
             locale = this.localizationProvider.getAvailableLanguages().some(e => e.languageId === locale) ? locale : 'en';
             this.localizationProvider.setCurrentLanguage(locale);
             res.send(this.localizationProvider.loadLocalization(locale));
         });
     }
-
 }
diff --git a/packages/plugin-ext/src/main/node/plugin-ext-backend-module.ts b/packages/plugin-ext/src/main/node/plugin-ext-backend-module.ts
index dfcb84e349c2b..57d6e6ffef50f 100644
--- a/packages/plugin-ext/src/main/node/plugin-ext-backend-module.ts
+++ b/packages/plugin-ext/src/main/node/plugin-ext-backend-module.ts
@@ -40,8 +40,10 @@ import { PluginTheiaEnvironment } from '../common/plugin-theia-environment';
 import { PluginTheiaDeployerParticipant } from './plugin-theia-deployer-participant';
 import { WebviewBackendSecurityWarnings } from './webview-backend-security-warnings';
 import { PluginUninstallationManager } from './plugin-uninstallation-manager';
+import { LocalizationBackendContribution } from '@theia/core/lib/node/i18n/localization-backend-contribution';
+import { PluginLocalizationBackendContribution } from './plugin-localization-backend-contribution';
 
-export function bindMainBackend(bind: interfaces.Bind): void {
+export function bindMainBackend(bind: interfaces.Bind, unbind: interfaces.Unbind, isBound: interfaces.IsBound, rebind: interfaces.Rebind): void {
     bind(PluginApiContribution).toSelf().inSingletonScope();
     bind(BackendApplicationContribution).toService(PluginApiContribution);
     bind(WsRequestValidatorContribution).toService(PluginApiContribution);
@@ -87,4 +89,7 @@ export function bindMainBackend(bind: interfaces.Bind): void {
 
     bind(WebviewBackendSecurityWarnings).toSelf().inSingletonScope();
     bind(BackendApplicationContribution).toService(WebviewBackendSecurityWarnings);
+
+    rebind(LocalizationBackendContribution).to(PluginLocalizationBackendContribution).inSingletonScope();
+
 }
diff --git a/packages/plugin-ext/src/main/node/plugin-localization-backend-contribution.ts b/packages/plugin-ext/src/main/node/plugin-localization-backend-contribution.ts
new file mode 100644
index 0000000000000..2f5c3aff101a6
--- /dev/null
+++ b/packages/plugin-ext/src/main/node/plugin-localization-backend-contribution.ts
@@ -0,0 +1,42 @@
+// *****************************************************************************
+// Copyright (C) 2021 TypeFox and others.
+//
+// This program and the accompanying materials are made available under the
+// terms of the Eclipse Public License v. 2.0 which is available at
+// http://www.eclipse.org/legal/epl-2.0.
+//
+// This Source Code may also be made available under the following Secondary
+// Licenses when the conditions for such availability set forth in the Eclipse
+// Public License v. 2.0 are satisfied: GNU General Public License, version 2
+// with the GNU Classpath Exception which is available at
+// https://www.gnu.org/software/classpath/license.html.
+//
+// SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
+// *****************************************************************************
+
+import { inject, injectable } from '@theia/core/shared/inversify';
+import { LocalizationBackendContribution } from '@theia/core/lib/node/i18n/localization-backend-contribution';
+import { PluginDeployer } from '../../common/plugin-protocol';
+import { PluginDeployerImpl } from './plugin-deployer-impl';
+import { Deferred } from '@theia/core/lib/common/promise-util';
+
+@injectable()
+export class PluginLocalizationBackendContribution extends LocalizationBackendContribution {
+    @inject(PluginDeployer)
+    protected readonly pluginDeployer: PluginDeployerImpl;
+    protected readonly pluginsDeployed = new Deferred();
+
+    override async initialize(): Promise<void> {
+        this.pluginDeployer.onDidDeploy(() => {
+            this.pluginsDeployed.resolve();
+        });
+        await super.initialize();
+    }
+
+    override async waitForInitialization(): Promise<void> {
+        await Promise.all([
+            super.waitForInitialization(),
+            this.pluginsDeployed.promise,
+        ]);
+    }
+}
diff --git a/packages/plugin-ext/src/plugin-ext-backend-electron-module.ts b/packages/plugin-ext/src/plugin-ext-backend-electron-module.ts
index 78926963336a3..ca1fd59d6bce0 100644
--- a/packages/plugin-ext/src/plugin-ext-backend-electron-module.ts
+++ b/packages/plugin-ext/src/plugin-ext-backend-electron-module.ts
@@ -18,7 +18,7 @@ import { ContainerModule } from '@theia/core/shared/inversify';
 import { bindElectronBackend } from './hosted/node-electron/plugin-ext-hosted-electron-backend-module';
 import { bindMainBackend } from './main/node/plugin-ext-backend-module';
 
-export default new ContainerModule(bind => {
-    bindMainBackend(bind);
+export default new ContainerModule((bind, unbind, isBound, rebind) => {
+    bindMainBackend(bind, unbind, isBound, rebind);
     bindElectronBackend(bind);
 });
diff --git a/packages/plugin-ext/src/plugin-ext-backend-module.ts b/packages/plugin-ext/src/plugin-ext-backend-module.ts
index aec5f0b3d32cc..6093561e11ff1 100644
--- a/packages/plugin-ext/src/plugin-ext-backend-module.ts
+++ b/packages/plugin-ext/src/plugin-ext-backend-module.ts
@@ -18,7 +18,7 @@ import { ContainerModule } from '@theia/core/shared/inversify';
 import { bindHostedBackend } from './hosted/node/plugin-ext-hosted-backend-module';
 import { bindMainBackend } from './main/node/plugin-ext-backend-module';
 
-export default new ContainerModule(bind => {
-    bindMainBackend(bind);
+export default new ContainerModule((bind, unbind, isBound, rebind) => {
+    bindMainBackend(bind, unbind, isBound, rebind);
     bindHostedBackend(bind);
 });