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You can get celebi on japanese colosseum bonus disc and jirachi with the USA bonus disc. For celebi you need jap colosseum too, and you can play that on an english gamecube with the help of a "free loader" disc.
You can get ho-oh in colosseum too, lugia in "gale of darkness", but deoxys and mew are gonna be tricky. you're gonna need italian emerald to get a legit deoxys. you can send it in to nintendo of italy and they'll load the aurora ticket on your cart. can anyone confirm if they take international orders though? otherwise you can "glitzer pop" to both the mew and deoxys events on only NON-ENGLISH copies of emerald. look up glitzer popping for more info.
and that's about it! i got myself everything except the legit deoxys event. when i can confirm that they take international orders, i'll send mine in and make mew the only pokemon obtainable via glitching.