The inhabitants of most Lands speak a degenerate form of Imperial, the tongue of the True Empire. Of course, everyone claims that their version of the tongue is the one closest to the original. The version spoken in and near /Glain does seem to be fairly pure, given the relative ease with which Glaen scholars can translate documents which date back to the Imperial era. The differences between dialects can be fairly vast, but a few days for determined speakers is generally enough to gain a simple idea of what's being said in another dialect.
The language itself is quite easy to learn, which contributes to its continued popularity as lingua franca of the Lands. It's particularly rich in words and concepts for describing relationships between things, another reason it's popular in the 10,000 Disjoined Lands, as much navigation is done on this basis due to the changing nature of the Lands and the Paths between.
Imperial script is phonetic, whith approximately 250 symbols representing the various sounds. Words are spelled exactly as they sound, which can interfere with standard spellings, as various dialects will thus spell the same word differently.
A subset of Imperial with a large number of borrowed words from other trade cultures.
A very small and simple language, which means nearly anyone can speak it. Unfortunately, about the only things that can really be said in it are 'How much for that thing there', '10 silvers and that's cutting my own throat', and 'which way to the place to buy stuff'. Anything beyond simple haggling and the most basic navigation directions will start to pull in from other langauges more heavily and run the risk of miscommunication between speakers.