I feel gelflings would talk the same language in heavy populate areas that started diversifying the farther you were moving from their center, like, vapra, spriton and stonewood sharing one but if you are in the center of Ha'rar, the colloquialisms on there would be like american english vs australian one (sifa would be like this from the start), while grottan/drenchen is more like spanish vs italian ideal when comparing other clans, some in common words and structure, nothing else there
yes this is actually exactly what i already had in mind!
here’s some of the stuff about language from the PANON notes doc i have:
the gelfling language family consists of uhh the main one (of which vapran, sifa, stonewood & spriton are considered dialects), drenchen, dousan, and grottan. these are for the most part mutually intelligable (tree incoming).
lots of podling loanwords/shared words especially among spriton & stonewoods
gelfling living in the major population centers of their clans, especially those of high rank, are usually at least partially fluent in vapran.
dreamfasting bridges any linguistic gaps as it is not directly verbal. dreamfasters will percieve others' speech in whatever language they're most comfortable with.
dousan have their own ritual language, unrelated to the conversational (which shares its root with all other gelfling languages).
grottan resembles antiquated vapran, and includes some mystic loanwords. due to isolation, it's the most removed of the gelfling languages and is difficult to understand by most.
written language consists of the vapran letter-based script, with characters derived loosely from skeksis, as well as symbols used in dream-etching. most gelfling can only understand the latter.