BAGHDAD—For visitors here, it can be hard to say goodbye.

In Iraq, the English word hello has become entrenched in the parting protocol, usually as a decrescendo—HELLO, Hello, hello—until a call is disconnected or a door shut. Many Iraqis say they have no idea why.

The practice leaves newcomers perplexed. An official at the American embassy recalled when he was a new arrival and at the end of a long meeting his Iraqi counterparts shook his hand and said, “Thank you, hello, hello, hello, thank you.”

The official, feeling panicked, recalled thinking, “Whoa, wait a minute. Are we starting another meeting now?”

The way some Iraqis say hello to mean goodbye is just one of many peculiarities that make Iraqi Arabic unique among the Arabic dialects of the Middle East. The vernacular here echoes a mishmash of historical influences: ancient Islamic empires, British colonial rule and, more recently, Western-style consumerism and the internet.