The Main page template is used with the parameter 1 set to en which prevents translated content from being shown on the Main Page. The parameter should be removed. (Invalid parameters will lead to the page being shown in English, so there wouldn't be a resulting problem.)
Topic on Template talk:Main page
Thank you!
I note that you performed that exact opposite edit at Template talk:Main page#Display preferred language due to a request by Wargo. A decision should be made here, rather than there being hodgepodge oscillations at the request of individual users.
The edit at MediaWiki was wrong and unrelated to the request. At that time I should do this edit at Template:Main page.