What do you mean exactly?

Are you curious as to why some programs, like text editors manage to identify which programming language a piece of code represents? File extension, or even existence of certain keywords particular to a language can help identify the programming language used with a bit of parsing. After all, these are all heuristic methods that practically works quite well with sometimes quite accurate guesses but they are not necessarily correct.

I don't think Unix by itself recognizes the language used. For example, if you want to compile a C program you need to explicitly invoke 'cc'; while for a Perl program you need to invoke 'perl' (or as the top shebang line). There is no mystery in there.