What's the rule for which 'national identity adjective' suffix to use?

Netherlands = Dutch

The English Language, where the grammar is made up and the rules don't matter.

I can add:

[-er] New Zealander

Demonyms don't follow any particular rules, as far as I know. I'm an "-egian" myself.

Canada = Canadese (nuts fit in your mouth?)

I can tell you that this is called demonym, but I don't know the answer to your question... The Wikipedia page has a long list of suffixes, but no rules: https://en.m.wikipedia.org/wiki/Demonym

There is no common rule. It varies by the way the language evolved over time.

Also the word you are looking for is "Demonym"

There are no rules in English. Ask the people from each country what they prefer

I'm in Michigan, that makes me a Michigander. The rules are made up and the suffixes don't matter.

People from Iceland are only called Icelandic because “Icish” would sound a bit silly.

We're all Earthicans, no need to divide it up further than that

Denmark -> Dane

I guess that actually the other way around, Denmark : Dane's field/farm(there is a better English word for mark but can't remember)

It's based on what sounds best.

Find what sounds most natural, if that can't be found, go with what sounds the least catastrophically unnatural.

Just attach "man" to the end of all of them for maximum offence.

Americaneseish.

There is no rule. It just is whatever it is.

I was literally thinking about this yesterday… what’s someone from Belgium called? I couldn’t figure out an ending to add. Belgian?

People from Indiana are called hoosiers - this, like many things in English, doesn't have a hard and fast rule... the sounds at the end of the word certainly impact it, but there are exceptions. Just ask a Peruvian.

There is a Words For Granted podcast episode about that. Don't remember much tho. Have fun!

Afghani, Pakistani,

Meanwhile there is no specific demonym for people from the united states, you can say american buy that would also include every other north and south american country

So Philippines is Philippinese?