In Turkish, suffixes are formed according to Turkish vowel harmony, rules whereby most vowel sounds in a word are made either in the front of the mouth or the back, but not both.
So if the vowels in the root are formed in the back of the mouth (a, undotted ‘i’, o, u), as in banka (bank), you add -lar to make bankalar (banks).
If the vowels are made in the front of the mouth (e, i, ö, ü), you add -ler to tren to make trenler (trains).
Likewise, arabamız, ‘our car,’ but otobüsümüz, ‘our bus’.
The suffix is the same one, but modified according to vowel harmony.
It’s not nearly so weird as it seems once you get the hang of it, and it gives a nice mellifluous sound to Turkish sentences.
When I was a Peace Corps teacher in Turkey (more…), one of the first sentences I was taught was Hepinizi disiplin kuruluna vereceğim! (HEH-pee-nee-zee dee-see-PLEEN koo-roo-loo-nah veh-reh-jeh-yeem, “I will turn you all over to the Discipline Committee!)
If you read the phonetic transcription aloud, you’ll see how Turkish vowel harmony makes for a nice sound.
Luckily, my students at İzmir Koleji were well-behaved most of the time, and I didn’t ever have to say that sentence for real.