For example, on this article, I know have 2 grey texts in the "Langues" (languages) menu in the left part of the page: en-us and English.

First, what's the point of having two links for English language ?

Second, why is nothing is translated (en-us, English) giving strange sentences with a mix of French and English ?

Thrid, if I click on the en-us, I end up on an non existing domain https://en-us.wikipedia.org/wiki/Special:ContentTranslation?page=Adolphe+de+Cordoue&from=fr&to=en-us&targettitle=&campaign=interlanguagelink

Are there any tests performed with CX before releasing features on production wikis ?
When will you fix the many bugs that damage articles before trying to get more audience for CX ?