to quote Lewis Carroll 'words mean what I say they mean' so if that particular instrument is called a melodeon in England, then it's a melodeon. What it's called in other countries is irrelevant.

Possibly.

When I was in England, two row diatonic instruments that Marje wants to call "melodeons" were always referred to (in my hearing, anyway) as "button accordions"; in Ireland (again in my hearing) they were referred to as "button boxes". I found this usage familiar, as that was (and still is) the usage in Oz; it might (or might not) have been coincidental to my understanding of this usage that I had many dealings with Kurt Jacob, who was the Australian distributor for Hohner, and thus had exposure to the Hohner catalogue. As Hohner were the most frequently encountered button powered free reed instruments in Oz, that might explain why even the old bushies used the term "melodeon" to refer to only the single row instruments. Even then, the term applied only to the single row instruments that had the 'cotton reel' voice selectors; those without were referred to as "button accordions".

Because Mudcat is such an international forum it is probably helpful for posters to be aware of different usages of such terms so that confusions are minimised rather than multiplied. In a thread such as this one, which started with a question from someone who "appeared" to need explanatory information about an instrument type that was unfamiliar, I'd have thought that posters would go out of their way to be especially clear with their usage of terms. Which is why I (and others from Oz) have been careful to define our terms with reference to particular and known authorities.

Cheers, Rowan.