"There are many museums in İstanbul."
Translation:İstanbul'da çok müze var.
Yes the proper nouns needs an apostrophe if you are adding an inflectional morpheme to the noun but if its derivational morpheme you cant use apostrophe and also if you use an inflectional morpheme after a derivational morpheme you cant use apostrophe derivational morphemes (for nouns) -cı -lık -lı -sız inflectional morphemes (for nouns) -i -e -de -den -lar/-ler -ın/-in/-un/-ün
Huh... It was very hard to explain in english for a native turkish but i did . Have a nice day