1 It's very hard to determine that because statistics are hard to obtain. It is estimated that half the population of China are engaged in learning English in one way or another, and a third of Japan. However, such statistics are very hard to obtain because they would include those in ordinary education, those in the private ESL sector (which is not subject to census) and those learning by themselves. The most recent statistic I have seen for native speakers is half a billion.
2 I'd use 'have you been learning'