Which languages do you think in (your head)?

Same, despite English not being my native language, English is the language I think in and speak the most in my daily life so I guess it's natural for my brain to have adopted it as "primary language".

That being said, if I go home for a while and speak my native language extensively and hear it a lot then I naturally start thinking in my native language again.

Same with Spanish when I am living in Spain, I think in Spanish or both Spanish and English depending on the day.

So I think it varies a lot depending on my environement and how exposed I am to a language.

 

I'm the exact opposite: I usually think in my native language, Spanish, but sometimes when I get bored I start conversations in English in my head just to practise my vocabulary and skills.

 

Occasionally I think in Japanese but normally in English.

 

Mostly English (my home language) but occasionally Afrikaans (my second "first" language, lol) and sometimes French when I need to use it.

 

English. But I know a few French songs so I sing those too (mon coeur suvivra pour toi is a favourite)

 

I'm really impressed with anyone who thinks in something other than their native tongue. I've studied several languages and never even came close to thinking in any of them!

 

Most of the time I think in Czech, my native language, but sometimes I think in English as well, for example when I watch English movies or series and I comment on them in my head. The more I'm surrounded by English the more I tend to think in English. I bet I would be thinking more in English than Czech if living in an English speaking country.
Sometimes when I have nothing to do, I find myself trying to think in French, Polish or Slovak, but that usually fails after a while, because my level in these languages is not that good as my Czech or English, it's more like a playing a game in my head rather than actually thinking about stuff.