FWIW, I am not a muslim nor a native Arabic speaker but I "can read the Arabic alphabet to some degree".
Though if your numbers are correct, 2 billion sounds way too high
PEW Research and Wikipedia estimate are 1.9B.
[1] https://www.pewresearch.org/religion/2011/01/27/the-future-o...
FWIW, the usual estimate for worldwide adherents to Islam is ~1 billion.