I'm strangely attached to speaking English, possibly because it's the language I can express myself best

I still find this fascinating, that you can express yourself better in English than in German. Maybe not all that surprising considering how much time you spent in the UK, but still... it's something I have a hard time wrapping my head around, because my brain absolutely doesn't work like that. No language will ever be as central to me as German.

Weirdly, my answer to this is Irish Gaelic. No, I can't tell you why. It's just the vibe.

Ha! :D I don't think I've ever heard Irish Gaelic spoken. I probably should search, just to test the effect. :D

I might go for Icelandic, which is supremely charming and obviously not spoken by many people.

Another one that I've never heard spoken and now want to hear. :D

Arabic, maybe?

I get the reluctance re: new script, but I think it's probably very very easy compared to Chinese. (Isn't everything? :D )