hey i think its just add it in the DB, under playerinfo_spell or playerinfo_skill depend on what type of core you use.
it can be so you need to add.
like to add:
668 Language Common

either by class and race. 1 and 1 for homan warr same for all. so 1 2 for paladin and so on.

or your core are newer so you can add 0 0 for all race and classes.
or it even might use the new class and race masks. then you need to know the values for it. like 1 is human 8 its night elf. and so on.
if you added new races its works like the like duble of the lower one. so
1 2 4 8 16 32 and so on. so you need to know the ID of that race to put it in. like races 10 11 blood elf dranei.
9 11 warlock druid. and so on i think you will understand.

sorry bad english i get dyslexsia

hope it helped, i think it should help but i dont really know. you can allways turn on:
AllowTwoSide.Interaction.Chat     = 1
AllowTwoSide.Interaction.Channel  = 1

it should me it so all can understand all. not if a night elf speak there lang and undead speak there. thats not working. but i know it work with common and orcish they will be like one. so horde and ally can speak.
the channel one are for so they get one channel so instad of horde get oen and ally get one.