for anyone who interested in progress transfer for your mhxx.
here is the bruteforce method definitely will work:
(player slot swap, to be more specific.)
hexeditor open mhxx file, the offsets for the start of each save slot should be within the first 16 bytes (in little-endian, so the bytes are reversed but are the exact address to jump to when converted to big-endian), go to the offset for the player slot you want, take a 11d088 length block.(the rest of one player slot are in-game-quick-message string, no need to copy them, and u shouldn't, cuz xx and gu got different length for these shoutout messages)
open mhgu file, find the player slot again, paste it, let it overwrite all bytes.
if u got more than 1 slot to transfer, repeat the above steps.
NOTICE: this method wont transfer JP version dlc quest, dlc palico, but dlc palico you already hired are still available. u may also wanna clear the item box to get rid of those jp version dlc items, sell those xx only armory before transfer is also recommended.
btw, game may not be able to display jp characters(those palico) until the Chinese language patch arrive within 3 months.