This is the (almost) complete list of human languages in Mystara outer world (KW+RS+PWA)and how they are linked toghether (IMO).
Alphatian (Alphatian Empire, Minaean Coast, Glantri (Flaemish), Helskir,
Ochalea)
Thyatian (Thyatian Empire, Alatian Islands,Five Shires, Glantri, Heldann
(Hattian),Ierendi (for trade), Helskir, Karameikos, Norwold, Rockhome)
Atruaghin (Atruaghin clans, probably different from clan to clan, the Horse
Clan doesn't have a spoken language but uses hand signals.)
Darokinian (Darokin, Five Shires, Ierendi, Sind (not much))
Milenian (many dialects in Davania)
Thratian (Thyatian Hinterlands)
Denagoth (Denagoth)
Jennite (Jen, Esterhold, Minaean Coast)
Ethengarian (Ethengar, Glantri)
Traldaran (Karameikos, Glantri)
Averoignian (Glantri)
Kaelic (Glantri)
Urduk (Sind, Sind Desert, Barren Plain)
Sindhi (Sind, Sind Desert, Barren Plain)
Heldannic (Heldann, Northern Reaches, Norwold, Qeodhar, Wendar)
Hulean or Hulian (Hule)
Makai (Ierendi)
Thotian (Thotia)
Minaean (Minaean Coast)
Minrothad (Minrothad)
Nuar (Pearl Islands)
Karimari (Ulimwengu)
Yavdlom or Yavi (Yavdlom)
Ylari (Ylaruam)
Emerondian (Emerond)
Slag (Savage Coast Common tongue, used in the city-states, the Savage
Baronies, Robrenn, Eusdria, Renardry and Herath, known by traders in
southern Hule, northern Yavdlom, Bellayne and Tortles )
Slagich (City States)
Verdan (Vilaverde, Texeira)
Espa (the other Savage Baronies)
Ranax (Robrenn)
Eusdrian (Eusdria)
After reading the complete Timeline (thanks Daniel), I can draw the
following conclusion:
In Mystara there are 4 alien languages: Alphatian/Flaemish, Averoignian,
Kaelic (Klantrian Gaelic, by Chris Davies) and Emerondian.
We can recognize 4 main languages in Mystara: Oltec/Azcan, Tanagoro,
Neathar, Nithian.
>From Tanagoro come Nuar and Yavdlom (with Sheyallia Elvish influence).
>From Nithian originate Thotian, Ylari and Traldar, and from this come
Milenian and Slagich.
Neathar is the "father" of Makai, Urduk and Antalian. From the last one come
Eusdrian, Heldannic, Thratian and Thyatian.
>From the Oltec/Azcan group come Jennite, Sindhi (with Urduk influx) and
Minaean (with strong Milenian influence).
Slag is similar to Thyatian, Verdan and Espa.
Ethengarian and Denagoth aren't linked to any other language.
Darokinian should be a mix of Nithian, Traldar, Ylari and probably Sindhi,
Elvish and Thyatian.
Minrothad Patois is a mix of all languages.
Glantrian is (according to Chris) a technical language that takes words from
Flaemish, Averoignian, Traldar, Thyatian, Kaelic, Alphatian, 2 Elvish
dialects, Ethengharian and maybe Sindhi.