Honestly rapping in English for a Korean song isn't a bad thing. There are a lot of Korean songs that have English in them. Example 1: EXO-M and EXO-K's song Two Moons with SHINEE's Key. In Two Moons Key has an English rap that is at the end. Some Korean groups have members that aren't from Korea. Like EXO-M, Seventeen and Super Junior etc. Kpop isn't just for Korean people it's for everyone. Anyone can join. It's not against the law.