I disagree that Latinoaméricain follows convention. Most other contracted demonyms in French do not use -o- as a connecting vowel; hyphenation seems to be more common.
In the case of néozélandais, the -o- comes from the Greek neo-. I do not know why neo- is the convention rather than the Latin novo-.
Is -o- is the connecting vowel you would expect to see used with the word Latin? There are other french words that use -o- as the connecting vowel (e.g. démocratique), but those words usually have a Greek origin. Since the word Latin does not have a Greek origin, I would expect the connecting vowel to be -i- as in latinisme.
The origin of Amérique Latine is not necessarily related to the origin of latinoaméricano.
https://en.wiktionary.org/wiki/Appendix:French_demonyms https://en.wikipedia.org/wiki/List_of_adjectival_and_demonym... https://en.wikipedia.org/wiki/List_of_adjectivals_and_demony...
In the case of néozélandais, the -o- comes from the Greek neo-. I do not know why neo- is the convention rather than the Latin novo-.
Is -o- is the connecting vowel you would expect to see used with the word Latin? There are other french words that use -o- as the connecting vowel (e.g. démocratique), but those words usually have a Greek origin. Since the word Latin does not have a Greek origin, I would expect the connecting vowel to be -i- as in latinisme.
The origin of Amérique Latine is not necessarily related to the origin of latinoaméricano.