I would be absolutely shocked if this happens. Less than 1% of China's population speaks English beyond learning for business purposes. Making learning English illegal would be impossible to enforce, you would have to build additional infrastructure on the internet just to specifically block english courses. What you are suggesting is actually more complex.
I would never want to underestimate the ability of the CCP to scale solutions to political problems. It is, after all, the whole reason the party exists. We once thought the GFW would be impossible and laughed at it.
