You don't have to understand every language in the world to be able to identify the language in which words are written, you just have to know a little something about their alphabets and look for identifying marks.
Lover of linguistic lore James Harbeck shared his method of uncovering the language in question on The Week, which basically revolves around looking for accent marks and characters that are unique to specific languages:
Ã, ã: When you see this sign of a nasalized A (as in São Paulo), you're almost certainly looking at Portuguese, especially if the language looks a lot like Spanish.
Ă, ă: This A with a cup on the top is your surest way of knowing you're looking at Romanian (unless you're looking at Vietnamese, but read on for more about that). For further confirmation, look for Ț/ț and Ș/ș (that's T and S with a comma beneath).
Ő, ő; Ű, ű: These vowels that look like their hair is standing on end are the most unambiguous signs of Hungarian. The clever Hungarians just combined ó and ö to make a letter that means "long ö," and did same with ű.
Bonus: How can you tell Chinese and Japanese apart? There's one special character that will give away Japanese every time, and it's only fair to tell you. Japanese uses three writing systems, only one of which is the same as Chinese uses, but unless you know them, you're out of luck. But Japanese makes frequent use of the character の, which is a grammatical particle and does not exist in Chinese (Chinese characters are never round).
-Via Boing Boing