Learn Portuguese (Portugal): A comunidade luso-americana é bilingue. - The Luso-American community is bilingual.

In Portuguese compound adjectives, usually only the final word changes to match the gender and number of the noun. The first part (luso-) remains in its fixed, default masculine form, while the second part (americana) becomes feminine to agree with comunidade.

If we were talking about multiple communities, how would the compound adjective change?

It would become luso-americanas. Applying the exact same rule, only the second half changes to match the plural noun. The full sentence would be: As comunidades luso-americanas são bilingues.

Where does the prefix luso- come from, and can I use it as a standalone adjective?

Luso- comes from Lusitania, the ancient Roman province that covered much of modern-day Portugal. It is used almost exclusively as a combining prefix in compound words (like luso-brasileiro or luso-descendente). To just say "Portuguese" on its own, you use português.

Why doesn't bilingue change to show that comunidade is feminine?