Announcers in the stadium read off the names of the marching nations in French, English, (the official languages of the Olympics) and Mandarin Chinese with music accompanying the athletes as they marched into the stadium.
The Marshall Islands, Montenegro, and Tuvalu debuted at these Games,[1] and Serbia competed under its name for the first time after the 1912 Summer Olympics.
All nations in between marched in the order of their names in Chinese, the host country's language.
[2] Specifically: Two nations were ordered based on a different name: Three nations marched out of order: Brunei was excluded from the Games by the IOC shortly before the Opening Ceremony as no athletes had been registered.
Main reference: "List of flagbearers Bejing (sic) 2008" (PDF).