minhag - Yemenite Sefira

What is the source for the custom that Yemenite Jews people count Sefira in Aramaic? and why do they do it?

Answer

Otzar Ta'amei Haminhagim (cf.) explains that it is a remnant of a time when the spoken language was Aramaic. Since the primary purpose of s'fira is the keeping track of days it is preferable to count in a language that enables the counter to keep track - i.e. a language the counter understands.