For some time now I notice that interface messages are defaulting to English irrespective of whether translated version exist locally or in translatewiki.
For instance MediaWiki:Createacct-benefit-heading has translations in Arabic, Farsi, Hausa and French, but when you visit Special:CreateAccount where the message is displayed on each of these Wikipedias the message only shows English version. The first two Wikipedias host translation from translatewiki, the later two have local translations.
Example:
Visit ar:Special:CreateAccount
What you suppose to see in the first line beside username field =ويكيبيديا موقع يساهم فيه أشخاص مثلك.
What is shown now= ويكيبيديا is made by people like you.
The above is true to many messages on many Wikipedias other than English
