Google Input Tools for Chrome is a free browser extension which makes it easy to type in another language.
(To be clear, this is about entering text, not translating it. Using the Tools means you won't have to add a new system keyboard, but you'll still need to know the language you're trying to type.)
The extension requires some basic setup time, as you choose your preferred input methods and keyboards from the 90+ options available.
When it's time to start typing, simply click the extension icon, choose the input method/ language and click in a text box.
Depending on your selection, you may now be able to type on a virtual keyboard (90+ languages), draw in a handwriting recognition box (40+ languages), or simply type languages phonetically in English letters, and choose the correct word from a list of suggestions.
Please note, Chrome security features mean Google Input Tools can't work in the address bar, the Chrome Web Store or inside other Chrome extensions.
Also, the extension doesn't currently work inside Flash applications.