Draconic is the language of dragons. It uses its own distinct alphabet. Other native speakers include members of draconic and reptilian races, such as kobolds and wyverns. The language is also used as a primary means of arcane notation throughout Toril.

the Draconic word “rlin’d’kraukh” . . . which means, in Common: “small and somewhat intelligent mammal that is not a transformed dragon nor the favored of a dragon nor carrying a dragon egg or seed or other dragon relic, wittingly or unwittingly, that is, so far as I know, not openly and formally an ally, servant, slave, or worker-in-common-cause with a dragon, but that is a coerced or unwitting pawn I believe I can manipulate, whose behavior I can predict with fair confidence, because of its observed prior behavior under duress or manipulation of myself or other dragonkind.” (This is further colored by usage: a dragon would not use this word of someone they weren't eager to manipulate because they considered the creature to be manipulated relatively weak, unsuitable, or distasteful. They use it for ideal or useful pawns they anticipate using in successful ways.)

Note: by “small and somewhat intelligent,” what is meant is a creature habitually of smaller size than an older-than-newborn-hatchling dragon of my sort, that is intelligent enough to speak, remember messages and individual creatures met in the past, and master at least one articulate language. In other words, humans (and all of the demi-human and humanoid races).

There are certainly many more baffling words in the Realms, that have to do with faith-specific religious concepts or school-specific magical details . . . but they are specialized jargon, not difficult to translate at all for those who have the proper frames of reference (are of the right faith with the proper inner teachings, or have the right magical mastery and knowledge). For instance, it’s hard to describe the color green to someone who’s been blind from birth - - and it’s hard to describe the feel of the Weave when working with it in certain manners under particular conditions, to someone who’s never “felt the Weave” because they have no aptitude for the Art at all. But for someone who has shared experiences or guild initiations or technical training with the speaker, word meanings come more easily.