Criterion: 3.3.2 Labels or Instruction (AA)
The purpose of the interactive controls should be clear to the user.
The language selector uses the currently selected language as its label, which describes its current state but not its purpose. This button requires additional information that tells the user more about the purpose.
The user does not care about the currently selected language per se, but they care about whether the page is intelligible to them or not. Therefore, indicating the selected language is not a priority.
I intend to include “Language:” in the button label or reduce it to just “Language”, so that it describes the purpose of the language selector. In the case of a “Language:” prefix, I will probably shorten the language name to just the language (without the country) so that the UI does not take up too much space.
I note that we already have a similar solution implemented in the user preferences panel which says “My language (Language (Country))”.
Also: A detailed survey of various language selectors via Smashing Magazine.