No, you must only use English cards. You used to be able to play up to six foreign language cards with a reference, but now you must have a deck containing 60 English cards.
I went to Japan this LAST summer and got a buttload of cards... only to hear they're no longer legal a few weeks after I get back. I learned the hard way, with about 12 useful Primes and 4 or 5 full Legends.
Oh, really? Well now I don't feel so bad... some competitive players at my league were telling me to trade all of them before they went illegal. My bad ;P