Is there an application that shows in which languages the mobile application is written? I want to show a mobile app and it will tell me what language it is made in.
There is a chance that you could get something usable from decompiling an app's bytecode/binary, but it will never be easily human-readable code. I would highly recommend against trying to get anything useful out of compiled apps.
arent all apps either java, kotlin or swift?
There's also flutter, react native, ionic, xamarin, etc.
Well technically, those are frameworks and not programming languages.
well depends. react native still uses native components with a js bridge so that would actually not look different. flutter however draws components on the screen using skia so that would actually look a bit different if the components are new / unpolished. there are some tell - tale signs for a ionic project ( the loading screen ), etc.