and when you receive an email in a language other than your own, Gmail will show you a "Translate to" link to translate it to your default language. Click on it and gmail will replace the original message with a translated version.
What if you need to translate an entire thread? Despair not, you need not click "Translate message" for every message in your email thread. Just click on the "Translate conversation" link on the right hand side of the message. (Just above the ads).
The entire user experience is good and you can easily translate the messages. Gmail is also a bit smart and will show you the translate link even if the email has more than one language. Now all this, sounds good but what use is an easy to use to translation system if the translation is good. Can you trust the translation ? Can you safely depend on it? The answer is unfortunately a big "NO". It can give you an overall idea about the message but nothing more than that. You can see the results for a simple translation I did below. The language to be translated is Hindi.