There are some interesting papers about the idea that if you go back more than a few hundred years there is no possible way to learn the language. Just way to many natural changes. Have a look in the Foreign Languages thread
http://forum.escapeartists.info/index.php?topic=775.20and see how hard it is to figure out the pronunciation of
"Laissez les bon temps rouler"
There is also a book called "The Power of Babel" by Joh McWhortor showing how these changes are really uncontrollable.
The players respond with "Screw that! We're gonna jump back to Ancient Egypt and take over the world!"
So they load up on guns 'n' ammo and head for the Pharaohs. And as they're stepping out of their spent machine into the ancient desert, one of the player characters asks:
"Wait, do any of us speak Ancient Egyptian?"
I wouldn't worry too much - the Mongols, Huns, Germanic tribes, etc. probably didn't know too much Latin, Chinese or other languages.
If I could travel back in time, first I'd really want a very specific time period (+/- ten years) and place, so I could study up first. How many of us really know the political landscape 300 years ago in England, Japan, Africa? Doesn't really help to know the generalities of the Battle of Hastings in 1066, even in England.
I would only take "hand-powered" things, nothing that I had to reload. There are very good chances that even going back 30 years, I wouldn't find the right type of batteries, bullets or ballast, let alone 300.
Also, don't underestimate a village just taking all your stuff and getting rid of you. In 12-13th century Europe, strangers usually meant scouts or someone chased out of their own village - neither one good.
Then there's your own immune system (and all the bugs you carry) - I have no idea how well that would hold up, or how many people you might wipe out yourself...