There is a simple real-world test scenario that will accurately assess whether this box of tricks can translate simple phrases from "anyone who speaks English"; actually there are two.
The first test is a bit unfair, but Geordies are widely thought to be speaking some form of English.
The second is probably more useful. Have them call Dell tech support. If the contraption can accurately translate "Format your hard drive and re-install Windows" they've probably got a winner.
The reason this is a great idea is not so much the guaranteed testing of "English with an accent" - but rather that the same test material will be delivered regardless of query posed to the person at the other end of the phone.
I'm usually quite surprised by this innovative approach to repairing, say, Linux servers or network appliances, but it does allow for controlled testing using a single phrase.