Plurals
The plural suffixes in Turkish are -lar and -ler. We use the rules of Major Vowel Harmony to decide which suffix to use. Words whose last vowel is one of (a, ı, o, u) will get -lar added to it, while those whose last vowel is one of (e, i, ö, ü) will be followed by -ler.


Last Vowel Suffix
a, ı, o, u -lar
e, i, ö, ü -ler
Examples:
Araba - Arabalar (Car - Cars)
Kapı - Kapılar (Door - Doors)
Top - Toplar (Ball - Balls)
Soru - Sorular (Question - Questions)

Kalem - Kalemler (Pen - Pens)
Cami - Camiler (Mosque - Mosques)
Göz - Gözler (Eye - Eyes)
Türk - Türkler (Turk - Turks)