Made the Edit block string translatable.

lang/contexts.json

@@ -1,4 +1,5 @@
 {
 	"Rich Text Editor, %0": "Title of the CKEditor5 editor.",
-	"Rich Text Editor": "Title of the CKEditor5 editor."
+	"Rich Text Editor": "Title of the CKEditor5 editor.",
+	"Edit block": "Label of the block toolbar icon (a block toolbar is displayed next to each paragraph, heading, list item, etc. and contains e.g. block formatting options)"
 }

src/toolbar/block/blocktoolbar.js

@@ -208,10 +208,11 @@ export default class BlockToolbar extends Plugin {
 	 */
 	_createButtonView() {
 		const editor = this.editor;
+		const t = editor.t;
 		const buttonView = new BlockButtonView( editor.locale );
 
 		buttonView.set( {
-			label: editor.t( 'Edit block' ),
+			label: t( 'Edit block' ),
 			icon: iconPilcrow,
 			withText: false
 		} );