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Afghanistan and several countries around it each end in -stan or -istan. From what language group does that suffix come? I assume it means something like country or land, as in land of the Afghans or land of the Turks (Turministan, which leaves the question of the longer suffix, -inistan, which is found another time or two). How are the various languages therein related? Does the pupulace have a different name for their country?) How much is Arabic spoken in those countnries that are Islamic?

From the entry for -stan in the Online Etymology Dictionary linked to this site:
-stan
place-name element in Afghanistan, Pakistan, etc., from Persian -stan "country," from Indo-Iranian *stanam "place," literally "where one stands," from PIE *sta-no-, suffixed form of root *sta- "to stand" (see stet).

At stet we find
stet
direction to printer to disregard correction made to text, 1755, from Latin stet "let it stand," third person singular present subjunctive of stare "to stand, stand upright, be stiff," from PIE root *sta- "to stand, set down, make or be firm," with derivatives meaning "place or thing that is standing" (cognates: Sanskrit tisthati "stands;" Avestan histaiti "to stand;" Persian -stan "country," literally "where one stands;" Greek histemi "put, place, cause to stand; weigh," stasis "a standing still," statos "placed," stater "a weight, coin," stylos "pillar;" Latin sistere "stand still, stop, make stand, place, produce in court," status "manner, position, condition, attitude," stare "to stand," statio "station, post;" Lithuanian stojus "place myself," statau "place;" Old Church Slavonic staja "place myself," stanu "position;" Gothic standan, Old English standan "to stand," stede "place," steall "place where cattle are kept;" Old Norse steði "anvil," stallr "pedestal for idols, altar;" German Stall "a stable;" Old Irish sessam "the act of standing").

Thanks. Should have tried OED myself.
Any linguists know the answer to my other questions?