It was originally running windows 7 with English as the system language. Some software were installed while I was in Turkey, some (including windows 10 upgrade) were installed after I moved to Finland. Now I’m learning that my computer couldn’t handle this gracefully :)
// Edit:
Okay so the issue can be resolved as follows (Windows 10): Windows Settings -> Time & Language -> Language -> Preferred Languages -> Order it so that "English (United States)" is at the top
I previsouly had "English (Switzerland)" at the top. This order influences the "Apps & websites" setting at the top there.
With "English (Switzerland)" my section headings in the Store were French, e.g. "Films et TV" but with "English (United States)" at the top I get "Movies & TV". Of course the section headings, callouts, etc. otherwise are still a mixture of your MS Store region (German in my case) and the Windows display language (English in my case).
Why "English (Switzerland)" would result in French... I don't know.