What Army or DOD regulation covers english only in the workplace?

Question

I was told there is a regulation that say english is the only language that is to be spoken in the military workplace unless it is part of your officilal dutys to speak another language

Answer 1

It is official policy, but I couldn't quote you the Regs.

Answer 2

I highly doubt there is such a regulation. There have been many discrimination lawsuits about this.

I am a DoD employee working on a military base and I've never heard of an english-only policy.