I'm French and I live in England. I think in English because I am fluent enough for that (or rather I am fluent because I can think in English).
When I go back to France or talk with French people here I think in French but there always are expressions that more easily come up to mind in English for the first few days. Same when I come back to England, some expressions come more easily in French because I spent more time thinking in French the preceding week(s).
Of course there are always times when I can express a thought in French but not in English, or at least not as concisely, as while I may be fluent there still are expressions that are near impossible to translate and there are colloquialisms that I may not know or only have met often enough to understand them but not enough to have them spring to mind when talking.
I thought in English to make this post.
Et j'ai pense en francais pour cette phrase. Desole pour le manque d'accents mais mon clavier qwerty n'est pas pratique pour cela.
"I do not suffer from insanity, I enjoy every minute of it"
