some nationalities have a certain shape but they are exceptional:
-ish (mostly European): Irish, British, English, Scottish, Finnish, Polish, Spanish, Turkish...
-ese (mostly Asian): Japanese, Burmese, Chinese, Taiwanese, Vietnamese, Portugese
-i (mostly Middle Eastern and Asian): Bahrani, Iraqi, Israeli, Thai, Kuwaiti, Pakistani, Saudi
- an/ian: American, Italian, Indonesian, Australian, Canadian, Russian
-ch: French, Czech, Dutch, Korean
some others: Icelandic, Greek, Filipino, Swiss, Malagasy
hope it's of help!