Is there a way for “q=60” to mean “quaver=60”, for us Brits? And similar mnemonics for “minim” etc. 
No, at the moment, Ian, q = quarter, and e = eighth.
I never understand why some composers insist on q= because it is asking for problems. It’s bad enough when an engraving typo causes 60 years of performing something at the wrong speed, without making something ambiguous on purpose. 
I think the question is just about how you type it in. Press Q to get a crotchet, E for a quaver etc, which is a nice and obvious mnemonic unless you call them crotchets and quavers.
Yes, I wondered if Dorico might change mnemonic based on the user’s computer locale. A minor point in the grand (and very exciting) scheme of things!
No, please don’t! This is not a simple preference for a shortcut key. A Brexit from the convention that q means quarter-note would only bring confusion.