I don’t think I code switch, though I’m enough of a mimic that my accent drifts just slightly in some places. I’m very conscious while visiting the British Isles not to unintentionally mimic anybody; I’ve heard the Irish hate it when folks from away put on a fake brogue. When I’m in Wales I sometimes drift into a bit of a Glamorgan tone; I also learned the rudiments of the north-south split in Welsh dialect vocabulary so I may structure sentences differently in Llandudno than I do in Cardiff, but as my teacher was from the north east, that’s the dialect I tend to use and nobody doesn’t understand it (plus, they all speak English anyhow).
When I lived in California, my Canadian accent ('cause there’s just the one, eh?) was made fun of constantly by my classmates. It was especially bad after I’d visited home for a holiday, as my Canuck tones would recharge and I’d be nothing but “oot and aboot.”
This was fun when I was visiting relatives in Kentucky. But I got called out on it during my freshman year in college by an Indian student, and make sure that I don’t do it.
I’ve had to give a lot of training over Teams in the last two years, and I usually use transcription as well. It sometimes has some strange ideas of what I say, but it’s generally good.
My Belgian coworker says I don’t mumble like most Americans, and he’s not the only one.
I don’t use a lot of idioms at work. If I do, it’s because I’m having a discussion with someone and we’re trying to find the equivalent in French/German/Italian.
I’m another who, in the past, has changed accents depending on whom I’m talking to. I’m a natural mimic, which is why my language teachers always praised my accent. Most of the time I wasn’t even aware I was doing it unless someone asked where I was from. I had a female bartender bat her eyes at me and say “You have the cutest accent, where in the south y’all from?” Startled, I replied “Southeast Alaska”.
As I mentioned in the code switching thread, I also tend to change the vernacular I use, depending on who I’m talking to. I can speak fluent sailor, fluent construction worker, and reasonably fluent college-boy/learned person. The former has been very useful when talking to trades people, as it discourages price gouging.