"Mandarin (n)" with a capital "M," refers to a group of Chinese dialects spoken in about 4/5 of China and centering on Beijing. The mandarin orange uses the same name because it is native to the same general area (southeastern Asia)
mandarin (n): In Webster's 1828 dictionary, a mandarin was a magistrate or governor of a province in China. (Mind your history, now—Webster's was speaking of the imperial government, long before Mao Zedong). From that root, the meaning of "mandarin" took on a disapproving tone in modern English until it came to refer to a behind-the-scenes powerbroker in government. It also means a member of an elite intellectual group or one who believes in rule by the cultural elite. Calling someone a "mandarin" with a small "m" usually is not flattering.
Suggested Usage: In discussions of national and local politics, today's word often comes in handy: "Tanisha's squad of mandarin mommies overthrew the librarian to gain control of Children's Book Week." You might want say "I know a couple of linguistic mandarins who use their Word of the Day to fight what they perceive is catachresis (pronunciation and usage errors)." But please, say it with a smile!