The Old Tongue is still the dominant language of the North with Common only really spoken by those who have reason to interact often with southerners. The populations that can speak common are found at Bear Island, Mole’s Town, The Wall, Winterfell, White Harbor and around the Neck. There are now different dialects or variations of the Old Tongue which are spoken and are all largely comprehensible to each other — if only just in some cases.

High Tongue — the tongue used most by nobles, maesters and the like but is also very situational. Largely grew out of a response to the need to have specific language for court and academics. It is also the one most heavily linked with writing as the need to be able to communicate with the southern kingdoms and have records maesters could actually read forced them into reevaluating their writing system and adopting the southern one to suit their use. On the whole their alphabet is now largely the same as the one used for Common but with a few tweaks here or there. More static than Low Tongue.

Low Tongue — the most basic form south of the Wall, used by basically everyone, even nobles. It is the normal natural evolution of the language from when the first people settled in the North. Uses the same alphabet as High Tongue though it’s rarely needed since the majority of speakers are illiterate.

Marsh Tongue — the language of the Crannogmen, basically just Low Tongue with regional variations. Kinda somewhere between a dialect and the situation with Norwegian and Danish where they are totally comprehensible to each other but also still noticeably different.

Wildling Tongue — A catch-all for the variations of the Old Tongue spoken above the Wall. Some of them are comprehensible to Northerners but some are completely alien now. Generally the languages spoken closer to the Wall are the more understandable while the ones of the further or more isolationist groups are harder. Though some like the Thenns are actually reasonably understandable to the average Northerner as they’re using an older form of the language instead of a heavily altered one.

Since I’m not a linguist or conlang creating gigachad I use Gaelic as a rough stand in for the Old Tongue and kind of loosely wave at the existing variations in that language as kinda roughly the various forms that the Old Tongue takes.