In Gmail, there's now a link on the top of the message that lets you translate it to whatever language the user has their Gmail set to. You can also set it to translate to any language of your choice. Both the subject and body are translated, while the original message is maintained. You can switch back to the original message by hitting the translate link again. For those who ever wondered what those e-mail that are in a foreign language say, this tool can be very useful. However, even though the message may have been translated, it doesn't stay translated. You'll have to re-translate every time you're viewing that message again, which can be an annoyance to the end user.
In the case of Google Friend Connect's comment translate feature, all comments, even if they're in different languages, are translated into one language. This tool can be handy for those who wonder what those comments that are in a foreign language say.