You say "Fransız kızlar" and "Ingiliz hasta" but Türk bayrağı, Türk vatandaşı. What is the rule when the nationality becomes and adjective and when it is used as a noun? I was thinking that it is an adjective when talking about a person, but then "Türk vatandaşı" is not compatible with this rule. Or is there any rule to this?
Okay, I've meditated over it for a bit. Here's my conclusion:
The nationality is treated as an adjective ONLY when the next word denotes someone's profession. Ex.: Alman mühendis, İtalyan piyanist, Japon turist, Rus soprano etc.
In other cases, it's treated as a noun. Because the possession is intended. Thus the next word takes the possessive ending. Ex.: İspanyol halkı (public consisting of Spaniards), İngiliz hükümeti (government belonging to the English), Yunan mafyası (mafia consisting of Greeks), Bulgar vatandaşı (compatriot of Bulgarians) etc.
The words "kız" can be used either way without a difference in meaning. Türk kız = Türk kızı.
The words "kadın" and "erkek" are possessivized only if they refer to all the men and women of the nation. Ex.: Türk kadın = a Turkish woman, vs. Türk kadını = The Turkish women.
The word "adam" is never possessivized in this context: Macar adam.
Thanks! This is not an easy topic indeed :) . Actually I came over one more suggestion given on adjective and noun usage: For example, I could be "Türk vatandaşı", even my origin/family/parents are of different nationality but I have been given the Turkish citizenship. Or I could be "Türk Hemşiresi" if worked as a nurse but representing Turkey/Turkish hospital or organization (despite of my original nationality). I will continue my wondering... Turkish is a lovely language indeed :)