Learn Farsi: هیچ‌کس با نویسنده‌ی مطرود صحبت نمی‌کند.

It follows the ma-C1-C2-u-C3 pattern using the Arabic root ط ر د (T-R-D), which relates to expelling or driving away. By plugging those root letters into the pattern, you get مطرود (ma-T-R-u-D), which functions as a passive adjective or noun meaning "driven away," "rejected," or "outcast" (the person receiving the action).

Can مطرود be used as a noun on its own, or only as an adjective like in this sentence?

Arabic passive participles like this one are highly versatile. While it acts as an adjective here modifying نویسنده (writer) via the ezāfe, it is also commonly used as a standalone noun meaning "an outcast." For example, you could pluralize it as مطرودان or مطرودها to mean "the outcasts."

Why is the verb نمی‌کند negative when the sentence already starts with هیچ‌کس (nobody)?

Farsi strictly requires double negatives. Whenever you use a negative word like هیچ‌کس (nobody), هیچ‌چیز (nothing), or هیچ‌جا (nowhere), the main verb must also be in its negative form. A literal translation would be "Nobody does not speak."

Why is there an extra ی at the end of نویسنده‌ی?

The word نویسنده (writer) ends in a silent "he" (ه). When you need to link it to the adjective مطرود using an ezāfe, you cannot just attach the short "-e" vowel directly to the silent "he". The acts as a bridge, changing the pronunciation of the ezāfe to "-ye" (nevisande-ye).