This is a well-known Turkish love song from the days of the Ottoman Empire, according to my Turkish co-worker. Here's a rough translation:

As I was going to Uskudar, it started to rain (2X)
While I was going to Uskudar, my katip's setresi has mud on it (2X)
Katip has just awoken, and his eyes are sleepy. (2X)

Chorus:

Katip is mine and I am my katip's
It's nobody's business
His starched shirt becomes my katip

As I was going to Uskudar, I found a handkerchief (2X)
Into it, I put lokum (2X)
I looked awhile for my katip, but indeed he was next to me. (2X)

Repeat chorus

Katip: a member of the ministry in the Ottoman Empire; as such, he wears fine clothes and a starched shirt
Setresi: from Farsi, a long coat worn by government officials
Lokum: Turkish delight! (the candy, Spaw...)