Languages and races
At one time I thought I could put together a complete list of the languages and races for AD&D. The list was to accompany dialects, a new non-weapon proficiency. With all of the monsters, worlds, and changes over the different editions, a complete list would be rather long and confusing. If you wish to use dialects in your game, consult with your dungeon master. Now a few thoughts...
A hill dwarf from Krynn might not be able to understand a hill dwarf from Oerth. It is thought all elves descend from the same ancestors, so their languages across the worlds may not have changed much since they separated. Creatures like elementals may have a language which can not be spoken by anyone other than another elemental, but the language could be learned. The core dragons have a common language, however dragons introduced later on do not share that language.
Constructs and undead are not races. They nor lycanthropes have their own specific languages. Lycanthropes or the undead will speak the language they spoke before they were turned. Constructs would take commands in the languages of their creators.
AD&D 2nd Edition
(1 Slot, Relevant Ability: Int., Check Modifier: 0)
With this non-weapon proficiency, a character learns to speak up to three dialects of any language the character already knows. If there is a sub-dialect, the character needs to have the parent dialect. A character who knows the common language of elves could speak high elven, avariel, and gray elven with this proficiency. This proficiency also adds a +1 bonus to a personís reading and writing proficiency when it comes to the dialect as long as the person is proficient reading and writing the parent language.
D&D 3rd Edition
The character can speak localized variants of a language.
PREREQUISITES: Chosen language, Int 13+.
BENEFIT: The character gains the ability to speak three dialects of any language of your choice as if the character spent skill points to learn those dialects.
NORMAL: Without this feat, a character can only speak the core language and must spend skill points to learn a dialect.
SPECIAL: A character can gain this feat multiple times.