@bender-tags: 4.11.0, 2491, bug, mentions
@bender-ui: collapsed
@bender-ckeditor-plugins: wysiwygarea, toolbar, basicstyles, mentions

1. Set Polish keyboard on your OS.
2. Focus the editor.
3. Type `@trąba_`.

## Expected

Dropdown with `@trąba_bomba` entry shows up.

## Unexpected

Nothing happens.

4. Play with the rest of the names available after typing `@` to check if diacritic characters matching.
