Polyglot 3000 is a simple tool which, if provided with some sample text, will do its best to identify the language used (currently more than 470 languages are supported).
The program's interface is very straightforward, and essentially works just as you'd expect. The main feature is a text box; you copy text there from the clipboard (although you can enter it manually, too); and clicking the "Recognize language" button will name the most likely language, as well as providing a "Recognition accuracy" value which tells you how certain Polyglot 3000 is of its verdict.
In our tests this all seemed to work very well. Even when we only entered a few words, Polyglot 3000 still returned the correct language: the worst that seemed to happen is the "Recognition accuracy" figure would often tail off as the volume of sample text reduced.
Sometimes your copy-and-pasted text may be similar in several languages, however, and that can give Polyglot 3000 a few problems. If you click Recognition > Prominent Languages, though, the program will consider only the most likely major languages for your sample, which may help it to provide a more accurate result.