Help writing for a character who speaks English as a second language?

I learned English as 3rd language (German being my 2nd and probably best). My written English outside of academic work is garbage, my spoken English is OK I guess (I talk a lot to people when playing games and I've been told my accent is weird. Some ask me if Im scottish, others wonder if I'm from London, some think I'm from NZ)

A funny little thing is I learned to imitate various accents by listening to people and when I talk for prolonged periods of time I tend to mix them which probably sounds very amusing.

Mostly it becomes apparent that I'm not a native speaker when it comes to metaphors and figures of speech.

A word I can't pronounce for shit is "uncomfortable". I always butcher it. another nemesis of mine would be "cupboard". A friend from Birmingham told me it's [kɒbɪd] and it sounds absolutely horrendous when I say it.