could it be an autism thing that i want to use another language for everything? english isn't my first language but i prefer it. i read books only in english, i write my diaries in english, i would probably speak it too if i didn't have trouble with spelling. it's easier for me to identify and describe my feelings in english too, i think that might be because i have to go through a vocabulary in my head instead of just... feeling it. if that makes any sense.
Finding it easier to identify and express your feelings in English could be an autism thing. Many autistic people experience alexithymia (the difficulty or inability to identify or describe emotions) and having to translate between languages means that you’re putting more work into it which is likely why it’s easier for you to do so in English.
As for using another language in general, I’m not sure how this would be an autism thing.