I don't have better hyphenation (in fact I disable it completely), but here's a small hack that moves the files to USB storage (/.hyph/*.dic) so you can see and modify them directly (or rename them in order to disable).
Tested with my H2O using 3.12.0 firmware. Use at your own risk.
This hack is short lived; if you install custom hyphenDicts using a KoboRoot.tgz (or when another firmware update comes along), it will no longer be active and needs to be reinstalled. But you can always extract a hyphendict KoboRoot.tgz yourself and copy the dics to /.hyph/.
As for adding additional languages, you can add new hyph_*.dic files to /.hyph/ and then reinstall this hack (otherwise, the Kobo won't see the new file; it has to exist beforehand). And then hope the Kobo will actually use it.
EDIT: This hack moved here:
https://www.mobileread.com/forums/sho...d.php?t=266005