For those like me that thought this is wrong because of how big India is: according to the last census, only around 15% speak English as first/second/third language.
Though your intuition is correct: the amount of English speakers outnumbers that of Mandarin, but Mandarin significantly outnumbers English in terms of native-language speakers
The number of English speakers (in correct English).
Amount is for uncountable nouns, like butter, sugar etc.