Thread:Support/About MediaWiki:Apihelp-wbsearchentities-param-strictlanguage/uk/reply

Judging from the code, if useLanguageFallback is set to true, then the 'search program' searches for matches in other languages as well. So if it's set to false, it searches in the default language only. I can't be sure without looking at an instance of the message on the wiki. I'll ask my GCI mentor for help. Hang on...