I'm not disputing the use of the word "emergency". If that word was used instead of "mayday" in the UK it would be understood (although not standard). Of course, being a fluent English speaker I'd understand the word emergency and act accordingly (although the same could maybe not be said for a non-English speaker). Personally I think the internationally understood phrase should be used everywhere, but that's just my opinion.
"Roll the trucks" however is not standard phraseology in any country as far as I'm aware. IMHO it sounds very unprofessional, whether understood by the controller or not.