I've said this before, but I guess with the influx of additions to the community I should repeat this here.
While German, Japanese, Spanish and the like may not exist in Eorzea, other languages do exist, as noted in the Hyur race description:
What my group of roleplayers did in FFXI was act it out as though different languages were just different dialects, and autotranslate (PLEASE let there be autotranslate in FFXIV) were "commontonuge" or "trade language" terms that anyone speaking any dialect could understand.
Even if there aren't any other cannon languages in FFXIV, it's not hard to bend lore and add them by stating that different dialects of a language exist. To not do so could create racist divides among the RP community, and I don't want to see that. I like to think we have a little more depth than our "1337 or f41lz" uber no-life players.