@hughluotatebe the dative case is -e(-a), that y is a kaynaştırma harfi (thematic letter) there.
turkish language has 4 kaynaştırma harfi. these are; n, s, ş, y and we use these letters when a vowel-ending suffix is added to a vowel-ending word.
tbh i don't remember a grammar rule about how we choose between these 4 letters but in general we put y for one word, n for more than one word. for example; japonya(y)a, hollanda(y)a suriye(y)e mısır çarşısı(n)a, birleşik arap emirlikleri(n)e, topkapı sarayı(n)a