Hiya!
German native speaker here (slight Berlin accent), but I will be keeping my post in English, since most of the contributers to this thread seem to have only basic German, and writing in German tempts me to write in long, complicated run-on sentences which I understand are difficult for non-native speakers. (A German habit that is difficult to shed even when writing in English, as you can see.
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German as a language has some cool features, like being able to make up new words via compounds or nominalisation without sounding like you're using 'Buffy-speak'. But I still prefer writing in English, because it just sounds better to me. Less stilted, more lyrical. This may be because I'm hardly reading any fiction in German anymore these days, so fiction has become associated with the English language in my brain. So much so that I even think in English when I'm just plotting some story element while commuting in the morning, or trying to fall asleep at night. (My main reason for writing is to distract my brain from real life worries.)
About some topics I literally can't talk in German. I don't have the German vocabulary to discuss fandoms or media tropes, for example, because all my discussion of these topics happens in the anglosphere of the internet. Anything related to sex just sounds wrong and awkward in German (from dirty talk to discussions about LGTB issues - "schwul" is such an ugly word when you're used to "gay".) Of course, it could also be that this skewed perception just occurs because I've never been taught to be ashamed of English swear words. "Scheiße" sounds a lot worse to my ears than "shit", "ficken" a lot less classy and acceptable than "fuck".
Another thing I've noticed since I've switched almost my entire media intake to English a few years back is that I start to forget German words. Well, not forget, but in the middle of a conversation in German suddenly some everyday term will only come to me in English. Does anyone else have this problem? Or should I be worried about early onset Alzheimer's? (I was kind of hoping that would wait till I'm at least 60...)