It can translate 'to' and 'from' the following languages:
Arabic, Bulgarian, Catalan, Chinese, Croatian, Czech, Danish, Dutch, English, Filipino, Finnish, French, German, Greek, Hebrew, Hindi, Indonesian, Italian, Japanese, Korean, Latvian, Lithuanian, Norwegian, Polish, Portuguese, Romanian, Russian, Serbian, Slovak, Slovenian, Spanish, Swedish, Ukrainian, Vietnamese, and it can automatically detect the page language.
How to translate
You can quickly translate a word by alt clicking it, sections / paragraphs by alt clicking on highlighted/selected text. You can also translate the entire page with an option in the context menu. Google does the hard work, my extension just displays the output.
See the video tutorial on youtube it's rated 5 stars with over 800 ratings. The original got 120,000+ views. Feel free to scan on virustotal.com, jotti, or your favorite antivirus.
The translation quality depends on the language pairs you use. It's ultra fast and has some support for axioms and phrases. Please don't be retarded and say it doesn't provide a super accurate translation to some japanese site you want to read or write to like other assburgers have graciously done in the past. Words can have multiple definitions and it gets worse when you have languages where the symbol can have multiple pronunciations.
The firefox extension is like 6k, but I included a 25mb video tutorial which you can leave out with your torrent client. It's small because it just queries translate.google.com and lets it do the hard stuff. My extension just shows you its output.