Highlight the message. Then 'right click' on the highlighted message and you'll get a drop-down menu of choices. At the bottom of this is the choice "Properties". Click it.

A dialog box will open with two tabs; General and Details. Click on "Details".

Gaze in wonderment at all the details you never knew it took to get an e-mail from one place to another.

Stop gazing.

About 80% down towards the bottom you'll see a language line. It will say "X-NAS-Language: English" in most e-mails. If it says "Russian" the e-mail is up to no-good and is from the evil empire of dishonest people, unless you have pen pals that write you using the Cyrillic alphabet, which is popular throughout the old Soviet Union, Serbia, and a couple of other Balkan statelets.

PLEASE NOTE: Just because it says "English" doesn't necessarily guarantee it isn't from the evil empire of dishonest people.