Correct spelling, explanation: nationalities is a plural form of nationality, which is a noun. The word probably comes from the Latin form natio, which meant nation or people. However, nationalities probably entered English directly from the French word nationalite, which looks similar to the contemporary English form.

Definition of nationalities:
1. noun (plural form) – having the right to or belonging to some country or nation,
Various nationalities gathered in the main square to protest against the war.

Collocations with nationalities:
A few common collocations with nationalities include: different nationalities, various nationalities, and mixed nationalities.
Different nationalities have taken part in the project, which made everyone improve their English skills.
Our company hires various nationalities and that’s why well-developed communication skills are crucial.
We form an amazing team of mixed nationalities and that’s why our restaurant will be affected by cuisines from different cultures.

Incorrect spelling, explanation: the singular form of nationalities is nationality, which means that when we form a plural form, we need to change the -y letter into -i and then add an -es ending. However, some English users, when forming nationalities, forget about the -i letter before the -es ending and they create the incorrect form nationalites.