I natively speak Swedish but I’ve studied and used English for 4-5 years so I speak English fluently and would consider myself bilingual. I can think in either English or Swedish and I can mix sentences in Swedish and English freely. But I never think in a language that’s really a combination of those languages (what we would call svengelska in Swedish).

I’m also studying french and German but I’m not fluent in any of those languages. When using those languages (or at least German) I think in a language that’s truly a combination of that language and Swedish/English. I use words from all languages and construct sentences as I would in Swedish (reverse word order for questions, no weird German thing with adjectives at the end etc). This of course becomes a pain as soon as I have to express a thought to someone else.