Learn Swedish: Dina hemligheter är privata.

In Swedish, a noun that comes right after a possessive pronoun like dina (your) must be in the indefinite form. Even though we are talking about specific secrets, you use the indefinite plural hemligheter rather than the definite hemligheterna.

Why is the adjective privata instead of just privat?

Adjectives must match the noun they describe. Because hemligheter is plural, the adjective privat takes the plural ending -a to become privata.

How would this sentence change to use the generic possessive ens (one's)?

It would become Ens hemligheter är privata. Unlike dina which changes to match the noun (din, ditt, dina), the generic possessive ens never changes. It stays exactly the same whether the noun is singular, plural, an en-word, or an ett-word.

What is the singular form of hemligheter?

The singular is en hemlighet (a secret). In Swedish, nouns ending in the suffix -het are almost always en-words and form their plural by adding -er.