If you're here legally...then learn English and forgot the interpreter. America is your country now. English is what's spoken here.
It's just that simple.
For business and ordinary daily stuff, well and good.
ETA: Actually, not well and good. In many parts of the country - not just Silicon Valley or California - businesses that tell customers "Speak English!" tend to do less well that they could ... or go under.
In court, where misunderstanding a word or confusing singular-plural or incorrect verb tense could send a person to jail or a bankrupting civil judgment (and plenty of prosecutors and civil lawyers willing to take advantage of such mistakes), no, it's not that simple.