This is an idea, but what about supporting the open source program called "Language tool" in the editor? It is actively developed and might improve grammar on wikipedia:
https://languagetool.org/de/, https://github.com/languagetool-org/languagetool
Topic on Talk:New Developers
Hi @Biggerj1, please see https://www.mediawiki.org/wiki/How_to_report_a_bug as this page is not for idea collection. Thanks!
There was some work on that idea a few years ago. But it needs a new developer to actually make any progress. (I.e. It's on the gigantic list of things we all wish someone would work on. Volunteers appreciated, if you are or know any devs who could do it!). See Extension:LanguageTool and phab:T89107 for more info.
However it is certainly not in a good state to be listed on this page. Criteria for being listed on this page is given at New Developers/Featured Projects. Hope that helps.