Learn Turkish: Kimse çiğ soğan ve sarımsak yemezdi. - Nobody used to eat raw onion and garlic.

The verb stem is ye- (to eat). The -mez part is the negative aorist suffix, showing a general rule or habit ("does not eat"). Adding the past tense suffix -di shifts this general rule into the past. Together, they form the habitual past negative: "used to not eat" or "would not eat".

Why is the verb negative (yemezdi) if the subject kimse already means "nobody"?

In Turkish, negative pronouns like kimse (nobody/anybody) must always be paired with a negative verb. You can think of kimse as meaning "anybody" in this context, making the literal Turkish logic "Anybody used to not eat raw onion and garlic."

Could I use yemiyordu instead of yemezdi for "used to not eat"?

You can, but they have slightly different flavors. Yemiyordu (past continuous) means "was not eating" and can describe a habit during a specific past time. Yemezdi (aorist past) sounds stronger and more general, emphasizing a firm past habit or personal rule, much like saying "would never eat" in English.

Why don't soğan (onion) and sarımsak (garlic) take the plural suffix -lar?

When talking about food items in a general, categorical sense, Turkish keeps them singular. Adding -lar here would sound like you are talking about specific, individual whole onions and garlic bulbs rather than the food ingredients in general.