What is the default markup language for .wiki pages?

I have read from the documentation at Wiki | GitLab that several markup extensions are supported. For instance, .wiki, .mediawiki, textile, etc.

I am new to GitLab and converting an old wiki to conform with the current conventions. Therefore, it would be useful to me to know what Wiki “language” is triggered when files have a .wiki extension.

I’ve been using WikiText in Eclipse so far to edit the pages that I’m converting but it seems like MediaText defaults to Textile. I vaguely remember that in the past, I was using a set of tools that defaulted .wiki files to MediaWiki.

Can I safely consider that GitLab also defaults to MediaWiki? Or is MediaWiki “activated” only for files with an explicit .mediawiki extension?