"Otanj?bi omedet? gozaimasu" is "happy birthday" in Japanese. Birthdays are not celebrated in Japan to the same extent that tends to occur in countries in the Western world. In fact, no real tradition for celebrating birthdays existed in Japan until the 1950s.
One of the reasons why the celebrating of birthdays started to take hold in the 1950s, including the greeting of "Otanj?bi omedet? gozaimasu," arose from the U.S. and Allied occupation of the country following World War II. The primary reason birthdays specifically were not celebrated until rather recently in Japan is the tradition that all people grew older on New Year's Day.