Learn Portuguese (Portugal): Estes intercâmbios histórico-culturais são fundamentais. - These historical-cultural exchanges are fundamental.

In Portuguese, when an adjective is made up of two words joined by a hyphen, usually only the second word changes to match the gender and number of the noun it describes. Since intercâmbios is plural, the second part cultural becomes culturais. The first part, histórico, stays in its default masculine singular form.

If the noun were feminine plural, would the first part of the compound adjective change to match it?

No, the first element of a compound adjective almost always stays in its masculine singular form. For example, if we were talking about feminine plural roots (raízes), the phrase would be raízes histórico-culturais. Even if the second word had a distinct feminine form, like in feminine policies (políticas), the phrase would be políticas histórico-políticas.

Does the first word in a compound adjective like histórico-culturais always keep its accent?

Yes. Even though the first word (histórico) is locked in its masculine singular form, it keeps its original written accent because the two words are connected by a hyphen.

Why do both cultural and fundamental end in -is here?