In Islam, zakah has its own special characteristics and special rulings. It is different from tax paid to governments. Hence, income tax doesn’t replace the zakah.
Dr. Monzer Kahf, a prominent Muslim economist and counselor, states the following:  Zakah is one of the pillars of Islam, and it is a religious obligation with given characteristics, qualification, intention, recipients, etc. Are we being sure the religious authorities take 2.5% of our income as zakah? Taxes have different characteristics and uses.