I'm Norwegian, and I used to believe that all foreigners thought in Norwegian, but spoke another language. I even went so far as asking my mother to tell some English visitors to "speak the way they think"...
A childhood belief about foreign languages

others believed things like this
- I used to believe that if I spelled Norwegian words backwards, it would be English. I don't anymore...— Gudrun
- I used to believe that foreigners' ears translated English words to their own languageAnon
- I used to believe that, no matter what language other people spoke, that everyone thought in EnglishAnon
- I used to believe that the whole world spoke the same language- English.Anon
- I used to think that adults spoke an entirely different language (not English) when kids weren't around. — Swordfish
- I used to think that even people who spoke something other than English, thought in English— Peaches