For me worked editing the file /home/username/.config/gmameui, adding there lines (for titles ans snaps):
dir-title=/usr/local/share/games/mame/titles dir-snapshot=/usr/local/share/games/mame/snaps
You DO NOT have to put the final ";"
For me worked editing the file /home/username/ .config/ gmameui, adding there lines (for titles ans snaps):
dir-title= /usr/local/ share/games/ mame/titles /usr/local/ share/games/ mame/snaps
dir-snapshot=
You DO NOT have to put the final ";"