I'm just getting back into D&D after a 12 year (!!!) break and looking for a little advice on what Languages to choose for my Warlock.
She's a half elf sage who was an academic researcher who focused on the arcane. Her whole life she wanted to learn magic but was never able, so she researched ways to overcome this and eventually discovered a way to make a pact with Cthulhu. She believes she has found the way to tap into the powers of a sleeping god, though the truth is up to my DM.
Anyway, back on topic I am wonder what languages she would know. She automatically gets Elven and Common and has 3 more to choose. I will take Illuskan as that the region she's from and the other two I figured would be more exotic options relating to the research she undertook to uncover the pact ritual she performed in her background. Any suggestions would be greatly appreciated!
I think in the forgotten realms, the language of magic was Draconic. For rune magic you can also add Dwarven for the dwarf-runes.
Great, thanks for your help. 
I don't think that Draconic as the language of magic is specific to forgotten realms. If I recall correctly, the 3e PHB says that draconic is the language of magical study. I basically think of Draconic as the Latin of the default D&D worlds, because I associate Latin with the language of magic in modern settings.
In my home campaign, I use Draconic as the language of magic, similar to how Latin was the language of learning and education in Dark Ages Western Europe. YMMV and you may have a cooler idea come to mind.
Supernal and Infernal might be useful if you want to delve into divine spells and/or devil pacts, respectively.
Truenamers speak the Language of Creation, which does not translate into written form well (or might require hieroglyphics).
If you are FR-specific, look through The Grand History of the Realms and see what nations perform magical feats you think are awesome. Learn literacy in that tongue.