Not that many English-speaking Twitizens will need to have their tweets translated, but a new service in twinslator.com makes it possible.
The Twitter translation tool is powered by Google Translator and Twitter of course. Worth a look for sure should you be interested in tearing down language barriers and spreading your marketing message to Twitterers in other countries.
All you will need to do is type your tweet, select a language and press update to get the translation. Users have the option to "twin their tweet" (able to post both tweets on a twitter profile directly from the site, or post only the translated tweet to the profile.