Take backups. Try it.
NA to EU (English at least) tends to be more OK than Japan to other regions but is not assured of it. The DS does not have a universal save format, or header designated by Nintendo like some other systems (usually anything with a profile system or runs on a memory card) and the devs were free/expected to come up with their own setup on a per game basis (which can make things hard when it comes to matching up saves in the case of corrupt memory card but different discussion there).
Usual cause of fun and usually coming from or going to Japan is Japan has Japanese characters and traditionally games did not kick over 16 bit encodings to English language games, even on the DS where space no longer would have really been troubled.
Said names as well as being different encodings the game might not understand might also be longer in number of bits stored which means data surrounding it tends to get found in new locations.
Jumbled up locations due to extra data needing to be stored, or functions removed, also becomes a thing when going between regions -- the however many months to make it to EU from NA can mean bugs fixed, DLC of sorts wound in and features trimmed to satisfy local laws (gambling setups tending to be such things) or indeed kept in if parallel translations happened (Nintendo of Europe was a potent thing by the time of the DS, and wow I am old having just written that, and often did their own translations -- Advance Wars probably being the more noted example but there are others) and they changed things to go for US sensibilities.
Sometimes the game will also just check a serial.
You can sometimes fix this -- encoding is encoding, data if just shuffled by a few bytes can be padded out or trimmed, locations shuffled can be unshuffled, serials are serials...
How much effort this is vs just replaying the game is ever a fun one, and that is not covering what you do about checksums/hashes -- games since maybe the NES (though there are notable exceptions) have taken the data that encompasses the save, done a mathematical operation on it (add things up, parity, CRC, custom hash... it matters little) and had the results of that operation serve to confirm that the rest of the data was not corrupted because saves are inaccurate sometimes (and hackers are also a thing). You then get either to figure out what this particular checksum/hash is and also what data it covers (not necessarily from hash to end of file), or bypass it. On bypassing then for all the complexities of the hash the game in the end probably just does "[do hash routine] is result matching? if so then go, if not then stop and call corrupt save." and that can be more readily hacked to "if good then go and if bad then still go down the good path", with the added bonus that next time the game saves it will correct the hash for you and you can take that from your emulator and inject it back into the unmodified game.
I don't know what exists for Animal Crossing save editors and cheats but many times it can be useful to recreate a save using such things, and Animal Crossing does see a fair hacking community arise around it most times.
