technically my first language is english, but i also grew up speaking portuguese and english.
although people say i speak portuguese better, i see the advantage that i can communicate with most of the americas. (except for those who don’t speak either language or canadians who only know French)
Potentially Germany, where I grew up we said “Two idiots - one thought”. We have quite a lot if regional variety in these things.
My personal experience is that I just translate one idiom from one language / culture to the other without realising and still expect ppl. to know what I mean.