I would say apartheids, as in "the apartheids of South Africa and India." In this case, if the word "apartheid" was used, it would sound (to me, at least) like South Africa and India had gotten together and created a joint apartheid program.
Nazis is the plural form of Nazi.
in poetry, apartheid means the reactions to the period of violence, racism, oppression expressed in few words in the form of poems
Quotas is the plural form of the word quota. A quota is fixed or limited number of things or people.
Allies.
phoenixes
There is no plural form. Do and Do not are verbs
The plural form of him, her, or it is them. (objective pronouns)
Bridges is the plural form of bridge.
The plural form of "is" is "are."
The plural form of "I" is "we."
The plural form of "was" is "were."
"Groceries" is the plural form of "grocery."
"Beliefs" does not have a plural form, as it is already plural. Beliefs is the plural form of belief.
The plural form of mouth is mouths. The plural form of month is months. The Mounth is a range of hills in Scotland and does not have a plural form.
The plural form of the demonstrative pronoun 'that' is those.
The plural form is metres.
Trenches is the plural form.