When Google released their AJAX Language API last March, I had high hopes that a lot of cool new applications would be created that might allow me to experience parts of the web that were previously incomprehensible. There is potential for a number of applications that go far beyond simple localization.

“I’m not sure how fast the API is, but how about on-the-fly translation for instant messaging? Certainly Google’s machine translation is far from perfect, but imagine being able to have a conversation with someone in two languages where you’re only exposed to your native tongue,” I wrote at ReadWriteWeb.

Web developer Dave Trainer, who left a comment on my post about the Language API last March, has now released a really cool Greasemonkey script that adds (almost) instant translation to Firefox. Once you install the script, called GMtranslator and which you can download via Trainer’s blog, any site on the script’s white list displays a small translation controls box in the lower right hand corner of the screen.

The script can translate between English, Portuguese, Spanish, German, French, Italian, and Swiss. You simply click on the language you want to translate to, and then click on the text you want translated. You don’t have to tell the script which language you’re translating from — Google’s API can generally figure it out from context — and the text selection is done via JavaScript using the jQuery framework.

The script does have a few downsides. First, it’s not really instant. There is some lag while it pings the Google AJAX Language API and waits for a response, which means that my dream of instant, seamless translated chat is still not quite possible (but certainly plausible). Second, you can only select text to translate in blocks, rather than the whole page at once, which is sort of clunky. It would be great if you could set the script to automatically translate pages into the preferred language without having to manually select the text to be translated at all.

The translations themselves are only as good as Google’s machine translation, which means that they’re serviceable, but far from perfect. No professional translators are going to be put out of business. Still, GMtranslator for Greasemonkey is going onto my list of must-have Firefox add-ons and will definitely come in handy translating news on blogs from other countries.

Update: Google announced today that it has added a similar feature to Google Reader. The “Translate into my language” option will automatically translate blog posts into your native language. The feature is a 20% project and is presumably based on the same API that Trainer’s Greasemonkey script uses. Very cool.