I’m American (US) but when I lived in Germany, by the end of two years there I thought in German. I remember it, but there are two anecdotes that underscore it:

1. When I returned to the States, I’d occasionally not be able to remember the English word for some things. I lost “trashcan” for a good half hour, once.
2. I occasionally talk in my sleep, and for a few years after I returned my wife would sometimes tell me that I was speaking German.

I didn’t spend much time around English speakers when I lived there; I met my wife the year after I returned, and the person I was seeing when I lived in Germany had barely spoken English.

Both. Also some concepts may exist in one language and not the other.

Contrary to most people, most of my thoughts are in the form of a dialogue. When it’s a monologue, it’s still a monologue delivered to a crowd. So the language basically depends on who I’m thinking to speak to. Sometimes the mechanism is faulty so I snap out and realize I would never speak English to a certain person.

For context, I’m Italian, living in Germany with an American partner.

Certain topics (mostly household things), I’ll think in Irish.

Or sports… it’s easier for me to think “tá an cailis déanta aige” than “he fouled the player” because my sporting life has generally been through Irish.

Depends on the context of what I’m thinking about. I think that is the case for anyone that is truly fluent in more than one language.

My internal monologue is always in my native language but if I need to talk to somebody my brain switches to the language I need so I need no ‘translation’

I do not live in a English speaking country. And my mother tongue is not english.

I still sometimes think in English. As I use it a lot.

I dont think I have an inner monologue. I think in words only when imagining a conversation, or in this case, writing this comment. Otherwise I think in …images maybe?