Language artifacts for "The Elemental Magician"

I'm not inventing languages out of whole cloth for "The Elemental Magician" and I don't plan on using a lot of "untranslated" dialogue or terminology in the novel, but every foriegn culture does have a few lanaguage artifacts worth noting.

So!

In EM, the largest culture block is Malak, roughly translatable as "(The Land of) Kings". (The word 'king' singular would be melk, I think). It's a region with a common cultural background divvied up amongst an assortment of kingdoms and city-states that at various times get subsumed into one empire or another. The lingua franca for this region and much of the borderlands they trade with is Atenish. Atenish comes from Aten, one of the aforementioned kingdoms in Malak that was repeatedly politically dominant through the region's history although currently not so much.

Things I've done with Atenish:
1) The vocabulary is very loosely cribbed from semitic languages and really really ancient semitic-speaking language cultures (we're talking the days of Tyre and Sidon)
1b) As a result, the stems of some words are just the consonants (melk, malak)
2) Some adjective forms are formed with the suffix -oi (Malak, Malakoi; Skath, Skatoi)
3) Some adjective forms the suffix -(i)sh (Aten, Atenish; Brynnmar, Brynnmarsh)
4) I have one city, Rhudelin, where I've been using the adjective form -si (Rhudelin, Rhudelinsi)

I need some sort of rule governing those variable adjective forms. I'm thinking that the neutral/bare/archaic adjectival form is something like *-ois, and then it got modified depending on what sound it's following and possibly also syllable number.

Malak: disyllable, -(plosive) = *Malakois ~> -oi
Skath: monosyllable, -(fricative) = *Skathois ~> -oi
Aten: disyllable, -(nasal) = *Atenois ~> -ish
Brynnmar: disyllable, -(approximant) = *Brynnmarois ~> -sh
Rhudelin: trisyllable, -(nasal) = *Rhudelinois ~> -si

Needs more thinking, so leaving this here as a reference for now. More later.

Updated: from here on out, I'm changing Aten to Aden to avoid confusion with Egyptian religion. Aden would then generate the adjective "Adenish".

Think I've got the rules figured out now.
-oi is bare form, follows the typical consonants (plosives, fricatives)
-ish is the softened form that follows vowels and "vowelish" sounds (vowels, nasals, approximants)
-sh is a subtype of the softened form that follows rhotics
-si is a subtype of the softened form that occurs when the stem is three syllables or more.