Learn Italian: Il dialetto è una parte importante della cultura. - The dialect is an important part of the culture.

In Italian, when you talk about a broad category, a general concept, or an abstract noun (like "dialect" or "culture"), you almost always need to include the definite article. Therefore, "Dialect is..." must be translated as Il dialetto è....

Why is it una parte? I thought nouns ending in -e were masculine.

Nouns ending in -e can actually be either masculine or feminine. Parte happens to be a feminine noun, which is why it takes the feminine indefinite article una. You simply have to memorize the genders of nouns that end in -e.

Why doesn't the adjective change to importanta to match the feminine noun una parte?

Adjectives that end in -e in their dictionary form (like importante) don't change for gender. They only change for number: -e for singular and -i for plural. So it stays exactly the same whether it describes a feminine noun (una parte importante) or a masculine noun (un libro importante).

Why use della cultura instead of just di cultura?