Get Automatic Email Translations in Gmail
To get an email in a foreign tongue translated right in Gmail:

Open the desired email.
Pick the desired source and target languages (or, of course, Detect language for the former if you're not sure) in the translation bar that appears above the message's body.
If you do not see a translation bar:
Click the More down arrow next to the message's Reply button.
Select Translate message from the menu that comes up.
Gmail will remember the language you have selected as the target as the default for translations.
Click Translate message.