core / user_menu: aria-label attribute is not well supported on a div without role attribute

Steps to reproduce:

1. Open the user menu -> Language selector
2. Inspect the <div> containing language selector

Expected behaviour:

The <div>-element does not contain an aria-label attribute without also having a role-attribute.

Current behaviour:

The <div> have an aria-label attribute containing "Language selector". It does not have a role-attribute.

Why this is important:

As stated in the w3-documentation, <div> elements are not allowed to have the aria-label attribute without also specifying a role.

https://www.w3.org/TR/html-aria/#docconformance-naming