International Auxiliary Languages (also called IALs or auxlangs) have had mixed success in IB. The lingua franca of science is Latin, or more specifically, Latino Sine Flexione. It has become the standard for published scientific research.
Completely artificial languages, however, have fared worse. With so many languages already existing, people prefered to learn a few languages that were already understood than one which needed to gain ground. Add to that a cultural reticence to standardisation *there* (note that almost nobody has adopted the metric system) and you lose most incentive to have an IAL. (MP)
Volapük is apparently the most popular auxlang in IB -- though that's not saying much! Such languages are generally the province of a small group of diehard supporters of the Cause. Real people get along fine learning to communicate in four or five (or more) languages as a matter of course, simply because they live in countries or areas where four or five languages are spoken! The need for an artificial auxiliary language has not been felt, since the solution of using multiple natural languages has taken root. (PB, 32571)
A number of competing minor auxlangs seem to exist in IB, each with its own tiny core of diehard supporters. It has been jestingly stated that the R.T.C.'s main export product - apart from teddy-bears, chocolate, and small family zeppelins that have the unpleasant habit of exploding in mid-air - is IALs. Other examples seem to exist in Neokernopanto Nova (the One and Only IAL for the Entire World), VOS (an also-ran), and Jovinanto (another also-ran); not to mention Narbonido's "Fundamento".
Known IALs *there*
LWII, a frank "discussion" among proponents of various IALs