Learn Croatian: Sestra mi je visoka.

In Croatian, you can use the standard word for "my" and say Moja sestra je visoka. However, it is very common to use the small word mi (which literally means "to me") to show possession, especially for family members and body parts. It is a natural, conversational way to say that she is "sister to me."

Why are the words mi and je placed right after Sestra?

Both mi (to me) and je (is) are "clitics." These are short, unstressed words that have a strict rule in Croatian: they must take the second position in a sentence. Here, they group together right after the first word, which is Sestra.

Could I change the order and say "Sestra je mi visoka"?

No, the order must be mi je. When multiple clitics group together in the second position, they follow a strict sequence. Pronoun clitics like mi almost always have to come before the verb clitic je.

Why does the word for tall end in "-a" (visoka)?