diff --git a/packages/filesystem/src/browser/file-dialog/file-dialog.ts b/packages/filesystem/src/browser/file-dialog/file-dialog.ts
index 9b91cd7d2cc92..744507fd3b010 100644
--- a/packages/filesystem/src/browser/file-dialog/file-dialog.ts
+++ b/packages/filesystem/src/browser/file-dialog/file-dialog.ts
@@ -16,7 +16,7 @@
 
 import { injectable, inject, postConstruct } from '@theia/core/shared/inversify';
 import { Message } from '@theia/core/shared/@phosphor/messaging';
-import { Disposable, MaybeArray } from '@theia/core/lib/common';
+import { Disposable, MaybeArray, nls } from '@theia/core/lib/common';
 import { AbstractDialog, DialogProps, setEnabled, createIconButton, Widget, codiconArray, Key, LabelProvider } from '@theia/core/lib/browser';
 import { FileStatNode } from '../file-tree';
 import { LocationListRenderer, LocationListRendererFactory } from '../location';
@@ -244,7 +244,7 @@ export abstract class FileDialog<T> extends AbstractDialog<T> {
 
         this.appendFiltersPanel();
 
-        this.appendCloseButton('Cancel');
+        this.appendCloseButton(nls.localizeByDefault('Cancel'));
         this.appendAcceptButton(this.getAcceptButtonLabel());
 
         this.addKeyListener(this.back, Key.ENTER, () => {
diff --git a/packages/plugin-dev/src/browser/hosted-plugin-manager-client.ts b/packages/plugin-dev/src/browser/hosted-plugin-manager-client.ts
index 9d1af379a4e40..df66f76165e17 100644
--- a/packages/plugin-dev/src/browser/hosted-plugin-manager-client.ts
+++ b/packages/plugin-dev/src/browser/hosted-plugin-manager-client.ts
@@ -407,7 +407,7 @@ class OpenHostedInstanceLinkDialog extends AbstractDialog<string> {
         this.contentNode.appendChild(messageNode);
 
         this.appendCloseButton();
-        this.openButton = this.appendAcceptButton('Open');
+        this.openButton = this.appendAcceptButton(nls.localizeByDefault('Open'));
     }
 
     showOpenNewTabAskDialog(uri: string): void {
diff --git a/packages/plugin-ext/src/main/browser/commands.ts b/packages/plugin-ext/src/main/browser/commands.ts
index 4409035b70dc9..ea341cca59ff8 100644
--- a/packages/plugin-ext/src/main/browser/commands.ts
+++ b/packages/plugin-ext/src/main/browser/commands.ts
@@ -20,6 +20,7 @@ import { Command, CommandService } from '@theia/core/lib/common/command';
 import { AbstractDialog } from '@theia/core/lib/browser';
 import { WindowService } from '@theia/core/lib/browser/window/window-service';
 import * as DOMPurify from '@theia/core/shared/dompurify';
+import { nls } from '@theia/core/lib/common/nls';
 
 @injectable()
 export class OpenUriCommandHandler {
@@ -85,7 +86,7 @@ class OpenNewTabDialog extends AbstractDialog<string> {
         this.contentNode.appendChild(messageNode);
 
         this.appendCloseButton();
-        this.openButton = this.appendAcceptButton('Open');
+        this.openButton = this.appendAcceptButton(nls.localizeByDefault('Open'));
     }
 
     showOpenNewTabDialog(uri: string): void {
diff --git a/packages/plugin-ext/src/main/browser/dialogs/modal-notification.ts b/packages/plugin-ext/src/main/browser/dialogs/modal-notification.ts
index 3fb5f2d305668..f669ebfc47d78 100644
--- a/packages/plugin-ext/src/main/browser/dialogs/modal-notification.ts
+++ b/packages/plugin-ext/src/main/browser/dialogs/modal-notification.ts
@@ -20,6 +20,7 @@ import { AbstractDialog } from '@theia/core/lib/browser/dialogs';
 import '../../../../src/main/browser/dialogs/style/modal-notification.css';
 import { MainMessageItem, MainMessageOptions } from '../../../common/plugin-api-rpc';
 import { FrontendApplicationConfigProvider } from '@theia/core/lib/browser/frontend-application-config-provider';
+import { nls } from '@theia/core/lib/common/nls';
 
 export enum MessageType {
     Error = 'error',
@@ -91,7 +92,7 @@ export class ModalNotification extends AbstractDialog<string | undefined> {
         if (actions.length <= 0) {
             this.appendAcceptButton();
         } else if (!actions.some(action => action.isCloseAffordance === true)) {
-            this.appendCloseButton('Close');
+            this.appendCloseButton(nls.localizeByDefault('Close'));
         }
 
         return messageNode;