Thanks for your reply!
I now see https://gitlab.com/fdroid/fdroiddata/blob/46e5cce5/metadata/org.wikipedia.yml#L591 says
"we disable gradle abi splits because using the universal apk is easier for us for now."

Yes, that's the obvious choice. Currently, one can simply change the language-subdomain in the URL, since all the search parameters work cross-language (at least between de and en) - but it's still inconvenient, and inaccessible for non tech-savvy users