Learn Polish: Wielokulturowy zespół pracuje znacznie lepiej. - A multicultural team works much better.

It is built from the prefix wielo- (meaning multi- or many) and the adjective kulturowy (cultural). In Polish, compound adjectives where the first part determines or describes the property of the second part are written as a single, solid word without a hyphen.

If I need to decline wielokulturowy for a different case, do both parts of the word change?

No, only the very end of the word changes. It declines exactly like a standard adjective. For example, in the instrumental case, it becomes z wielokulturowym zespołem. The wielo- part stays permanently fixed.

Why use zespół for team here instead of drużyna?

Zespół is used for groups of people working together in a professional, musical, or project-based setting. Drużyna is almost exclusively used for sports teams or scout troops. Since this sentence is about working, zespół is the natural choice.

Can I use dużo instead of znacznie to say much better?

Yes, dużo lepiej is perfectly correct and very common in everyday speech. However, znacznie lepiej (significantly better) sounds slightly more professional and fits perfectly with a workplace context like a zespół.