If the fallback is for the search bar only, then it's OK, but if it were for the notice messages that appear on top of pages, then let them fallback to the default, English. --Mahmudmasri (talk) 12:40, 25 October 2017 (UTC)
Topic on Talk:Wikimedia Discovery/Disabling Messaging Fallbacks for Language Analysis
The change is only for search. Notice messages and user interface elements (like labels for links) are not affected.