[indigo945]

I don't know to what extent this has happened with German and Polish. They are, of course, (somewhat distant) cousins in any case, both being Indo-European languages.

But it is often the case that geographically close languages influence each other -- the term in linguistics is "sprachbund". If one is entirely honest, a lot of languages have taken vocabulary or grammatical features from one or more languages from other language families, rendering the entire idea of a language "family" (the word is here evoked to imply a pure genetic lineage) kind of suspect to begin with. But it still is how linguistics is commonly done today.

[brnt]

The basis for my very non-scientific observation is that I am a native Dutch speaker, who's conversational in German and has a Polish partner. German fits quite well in between Polish and Dutch in terms of features: Dutch has few, Polish has nearly all, and German has quite a few more than Dutch ;) Similarities between Dutch and German are more easily understood since they've a recent ancestor, but for Polish and German we must go back much further. Yet, my untrained eyes see a sort of continuity that seems to cross the language-family barrier, which could make sense because of that shared geography of German and Polish. I know that Poles have a history of fervent conversationalism that favors (grammatic) complexity, so perhaps it's a hobby that spilled over to German-speakers. Or vice versa (I know less of German cultural history).