Site settings: Authorized extensions 'Audio' button title text isn't displaying the text

At: /admin/site_settings/category/files?filter=%20Authorized%20extensions

Hovering over the Images, Videos and Documents buttons the title text ‘Allow extensions…’ is displayed. Hovering over the Audio button, the title text displayed is ‘[en_GB.admin.site_settings.file_types_list.add_types_title audio]’.