My sister and her friend used to believe that there was no such thing as the language 'English', they thought they spoke 'American' and 'English' was some kind of gibberish.
A childhood belief about foreign languages

others believed things like this
- 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
- At the age of four I believed I was soooo smart. I spoke TWO languages...English AND American!— Melinda
- 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
- I used to believe that "elemeno P" was a certain kind of "P" found only in the English language. Anon