Someone from Israel is called an "Israeli".
"Israel" is a proper noun. If you want to use it as an adjective, you use the word "Israeli", as in:Can you do any Israeli dances?
Yes. It's also a proper adjective.Yes. It's also a proper adjective.
The proper adjective for southwest is "southwestern."
The proper adjective is Haitian.
The proper adjective for Portuguese is "Portuguese."
Vietnamese is the proper adjective for Vietnam.
The proper adjective for Georgia is Georgian.
The proper adjective for George is Georgian.
Freudian is the proper adjective for Freud.
Mayan is itself a proper adjective.
The proper adjective for Siam is Siamese.