SRD said:Abilities:...
Intelligence: A creature can speak all the languages mentioned in its description, plus one additional language per point of Intelligence bonus. Any creature with an Intelligence score of 3 or higher understands at least one language (Common, unless noted otherwise).
Nail said:....just in case yer DM needs a rules quote: :\
SRD said:Mummies can speak Common, but seldom bother to do so.
SRD said:Wights speak Common.
SRD said:Wraiths speak Common and Infernal.
Actually....Mistwell said:...Undead have no languages in their description...

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.