diff --git a/packages/application-extension/src/index.ts b/packages/application-extension/src/index.ts
index 470d1fa1a6..5b937ea9ab 100644
--- a/packages/application-extension/src/index.ts
+++ b/packages/application-extension/src/index.ts
@@ -844,6 +844,19 @@ const treePathUpdater: JupyterFrontEndPlugin<ITreePathUpdater> = {
   autoStart: true
 };
 
+const translator: JupyterFrontEndPlugin<void> = {
+  id: '@jupyter-notebook/application-extension:translator',
+  requires: [INotebookShell, ITranslator],
+  autoStart: true,
+  activate: (
+    app: JupyterFrontEnd,
+    notebookShell: INotebookShell,
+    translator: ITranslator
+  ) => {
+    notebookShell.translator = translator;
+  }
+};
+
 /**
  * Zen mode plugin
  */
@@ -920,6 +933,7 @@ const plugins: JupyterFrontEndPlugin<any>[] = [
   topVisibility,
   tree,
   treePathUpdater,
+  translator,
   zen
 ];
 
diff --git a/packages/application/src/panelhandler.ts b/packages/application/src/panelhandler.ts
index 356a74cacb..212baa9abb 100644
--- a/packages/application/src/panelhandler.ts
+++ b/packages/application/src/panelhandler.ts
@@ -79,20 +79,20 @@ export class SidePanelHandler extends PanelHandler {
     this._widgetPanel = new StackedPanel();
     this._widgetPanel.widgetRemoved.connect(this._onWidgetRemoved, this);
 
-    const closeButton = document.createElement('button');
+    this._closeButton = document.createElement('button');
     closeIcon.element({
-      container: closeButton,
+      container: this._closeButton,
       height: '16px',
       width: 'auto'
     });
-    closeButton.onclick = () => {
+    this._closeButton.onclick = () => {
       this.collapse();
       this.hide();
     };
-    closeButton.className = 'jp-Button jp-SidePanel-collapse';
-    closeButton.title = 'Collapse side panel';
+    this._closeButton.className = 'jp-Button jp-SidePanel-collapse';
+    this._closeButton.title = 'Collapse side panel';
 
-    const icon = new Widget({ node: closeButton });
+    const icon = new Widget({ node: this._closeButton });
     this._panel.addWidget(icon);
     this._panel.addWidget(this._widgetPanel);
   }
@@ -150,6 +150,13 @@ export class SidePanelHandler extends PanelHandler {
     return this._widgetRemoved;
   }
 
+  /**
+   * Get the close button element.
+   */
+  get closeButton(): HTMLButtonElement {
+    return this._closeButton;
+  }
+
   /**
    * Expand the sidebar.
    *
@@ -283,6 +290,7 @@ export class SidePanelHandler extends PanelHandler {
   private _widgetPanel: StackedPanel;
   private _currentWidget: Widget | null;
   private _lastCurrentWidget: Widget | null;
+  private _closeButton: HTMLButtonElement;
   private _widgetAdded: Signal<SidePanelHandler, Widget> = new Signal(this);
   private _widgetRemoved: Signal<SidePanelHandler, Widget> = new Signal(this);
 }
diff --git a/packages/application/src/shell.ts b/packages/application/src/shell.ts
index 36b754c0fd..96b7c4b66a 100644
--- a/packages/application/src/shell.ts
+++ b/packages/application/src/shell.ts
@@ -3,6 +3,7 @@
 
 import { JupyterFrontEnd } from '@jupyterlab/application';
 import { DocumentRegistry } from '@jupyterlab/docregistry';
+import { ITranslator, nullTranslator } from '@jupyterlab/translation';
 
 import { find } from '@lumino/algorithm';
 import { PromiseDelegate, Token } from '@lumino/coreutils';
@@ -179,6 +180,27 @@ export class NotebookShell extends Widget implements JupyterFrontEnd.IShell {
     return this._mainWidgetLoaded.promise;
   }
 
+  /**
+   * Getter and setter for the translator.
+   */
+  get translator(): ITranslator {
+    return this._translator ?? nullTranslator;
+  }
+  set translator(value: ITranslator) {
+    if (value !== this._translator) {
+      this._translator = value;
+      const trans = value.load('notebook');
+      this._leftHandler.closeButton.title = trans.__(
+        'Collapse %1 side panel',
+        this._leftHandler.area
+      );
+      this._rightHandler.closeButton.title = trans.__(
+        'Collapse %1 side panel',
+        this._rightHandler.area
+      );
+    }
+  }
+
   /**
    * Activate a widget in its area.
    */
@@ -324,6 +346,7 @@ export class NotebookShell extends Widget implements JupyterFrontEnd.IShell {
   private _rightHandler: SidePanelHandler;
   private _spacer: Widget;
   private _main: Panel;
+  private _translator: ITranslator = nullTranslator;
   private _currentChanged = new Signal<this, void>(this);
   private _mainWidgetLoaded = new PromiseDelegate<void>();
 }