Porting a translation patch, including between systems, has been done before. Most troubles tend to come in screen size differences leading to different line lengths, in addition to whatever of the usual font/encoding issues you have and any additional/untranslated text in the newer version if they decided to expand something or include more of the original that might have otherwise been dropped.
I would not put money on the script order remaining the same either so be prepared for that.
But yeah fairly standard translation*, however without the need to always have a translator on hand. You might want some skill in presumably Japanese just in case, though English to English is viable enough -- if people are going to the effort they do tend to want the absolute best version which tends to mean starting with the original.
*find text in Saturn version, figure out its encoding, make export table, export, find text in PS2 version (might be the same file names or similar), figure out encoding and if there are any things lacking in it, sort any potentially lacking aspects, make import table, overwrite text accordingly, and fix pointer/line length issues (you might be able to export the pointers from the original and do something, however if extra text gets in the way then probably not). If you need to fix any localisations (think turning hamburger back into sushi) then you also get to do that.
Only "easy" way of doing it would be if you got lucky and it was a fairly standard format (very much doubt for both Saturn and PS2) or someone made a tool for it, which I doubt happened here. Being a Sega game I don't know if this made it to PC or anything, it did appear on the PS3 after all, where someone could have done something, however for this sort of game if it does not say Fire Emblem or made by Square (Enix) on the title screen then you are probably out of luck as far as tools go.