Questions & Answers about Kış günleri huzur veriyor.
This is actually two suffixes stuck together:
1) -ler is the regular plural marker, so günler means “days.”
2) -i here is the 3rd-person singular possessive suffix in a noun-noun compound. In Turkish you can form “X of Y” in two main ways:
• Genitive-possessive: kışın günleri (“the days of winter,” literally “winter’s days”)
• Noun-noun compound with possessive on the second noun: kış günleri (also “winter days” or “winter’s days”).
Both mean the same thing; the -i on günleri shows that the days “belong” to winter.