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You are right and wrong. You do need the national dex ( but i dont know how to get it) and you can trade a japanese pokemon to an english game. The game translates everything except the name.
I really need the national dex code because if you have that you are able to trade mew from emerald (j) to R/S (US or E) then to FR/LG (US or E). Once on the US or E version you are able to put it on colosseum.