Learn Turkish: Yavaş yavaş kutu kutu lokum yedik. - We slowly ate boxes of Turkish delight.

Repeating an adjective is a common way to turn it into an adverb of manner (describing how an action is done). While yavaş means "slow", the reduplication yavaş yavaş means the action of eating happened "slowly" or "gradually".

Does repeating a noun like kutu have a different effect than repeating an adjective?

Yes! When you repeat a noun, it emphasizes abundance, variety, or groups. Here, kutu kutu means "box after box" or "boxes of". It is a colorful way to show that you ate a lot of boxes, rather than just using the standard plural form kutular.

Since kutu kutu implies plural boxes, why isn't lokum pluralized as lokumlar?

In Turkish, when a word or phrase already indicates a plural quantity or abundance (like a number, or in this case, the reduplicated kutu kutu), the noun that follows it must stay singular. So we say kutu kutu lokum instead of kutu kutu lokumlar.

Why don't we use the accusative case here and say lokumu yedik?

We leave lokum in its bare dictionary form because it is an indefinite direct object. You are eating boxes of Turkish delight in general, not a specific, previously mentioned batch. If you were talking about eating "the" specific Turkish delight, you would need the accusative suffix.