Learn Spanish (Latin America): Mi amiga habla francés.

Hablar (to speak) is a regular -ar verb. To use it, we drop the -ar and add an ending that matches who is doing the action. Since mi amiga is a "she" (third-person singular), we add the ending -a to make habla.

How do we know the friend is female?

The word amiga ends in -a, which tells us she is a female friend. If you were talking about a male friend, it would be amigo.

Does mi change because amiga is a feminine word?

No! The word mi (my) only changes if you are talking about more than one thing or person, in which case it becomes mis (like mis amigas). It stays exactly the same for both masculine and feminine words, so you say mi amiga and mi amigo.

Why isn't francés capitalized?

Unlike in English, Spanish does not capitalize the names of languages or nationalities. Words like francés (French), inglés (English), and español (Spanish) are always written with lowercase letters unless they are the very first word in a sentence.