Japanese? Well I know Pikachu... and probably stuff like Pachirisu maybe
But mainly the germany names and very often the english names (due to hanging out on english messageboards)
Although I only really mastered the names in gen 1 when Pokemon was the biggest thing ever to me and my friends. Gen 2 is mostly okay, I have big holes in Gen 3 and Gen 5, I am really bad at Gen 4. Also, because I hang out too much at those english message boards I can't really keep the english and the german names apart.
One of my favorites of gen 5 is either symvolara or sigilyph, but I can't say, which is german and which is english. I always call Ramoth Volcarona, And Elfun is Whimsicott to me. Also the names are getting more and more ridiculous for me to remember.