Learn Turkish: Baharatlar çuvallarda yığın yığın duruyor. - The spices are standing in piles in the sacks.

Yığın means a pile or heap. By doubling it to create an ikileme (reduplication), it turns into an adverb of manner. It vividly describes that the spices are standing "in piles" or "pile upon pile," emphasizing abundance and the way they are physically arranged.

Why use the verb duruyor here instead of just saying they "are" in the sacks?

In Turkish, the verb durmak (to stand, stop, or stay) is frequently used to describe the location or resting state of inanimate objects. While English simply uses the verb "to be," Turkish prefers durmak to show that the spices are physically resting or sitting inside the sacks.

Could I use the locative case and say çuvallarda yığınlarda duruyor to mean "in piles in the sacks"?

No, stacking locative endings like that sounds very unnatural in Turkish. Using the reduplication yığın yığın is the native way to turn the noun "pile" into an adverb describing how the items are stored, avoiding clunky grammar.

Why does baharat take the plural suffix -lar here?

Although spice can be thought of as a mass noun (like sugar or salt), adding -lar to make baharatlar is very common when referring to multiple different types of spices, or a large, distinct variety of them in a physical setting like a market.