After two years' learning Arabic, I can read the holy Koran now. - I think it's fine as it is, but this is an unnatural expression and slightly awkward After learning Arabic for two years, I can read the holy Koran now. - Perfect as is. Very natural After two years of learning Arabic, I can read the holy Koran now. - Perfect as is. Very natural

All 3 have perfect grammar.

All three are correct. It´s an individual choice how you would like to come across, more natural or reserved