that would explain why at lvl 7 and 16 my iron sword got Firebrand I.
do we yet know the level ranges at which each enchantment( and level of enchantment) can accrue?
Yeah, it's luck based in a way.
The Symbols actualy mean something, to decode go here:
Long and compicated process: http://www.omniglot.com/writing/sga.htm
So decode, and if you don't like, you take your pick and put it again and the enchantment will change. Mr. Paulsoaresjr explains it in these 2 vids.