Version 7 of the program contains Spanish and English interface languages. This is the first version that does, because previously the dictionary was only available in English and it seemed pointless including any other languages if such a core feature was going to be English only.
Now I have a very usable copy of the dictionary translated into Spanish with the help of the Google Translation API. It is not perfect but it is definitely fit for purpose. I also tried to translate the interface using the same technique but the results were very disappointing. Basically the interface consists of short, terse phrases that lack any kind of context that that the translation engine can get to grips with. Is "Edit History" the history of edits or a command that lets you edit the history? This kind of ambiguity meant that I had to redo about half of the interface with my own somewhat dodgy Spanish. This is why it includes a mishmash of expressions with the "tú" verb form (mine) and the American sounding "usted" form (Google's). I am waiting for a Spanish friend to go through and tidy the whole thing up when she has the time to do so.
The result of the dictionary translation was much better, presumably because the definitions are whole sentences and that gives the translation engine a context to work with. There were some glaring mistakes which I had to apply bulk corrections to (for example "Chinese surname Man" universally translated to "Apellido chino Hombre", a similar thing happening with other surnames). I think I got the worst of these corrected. Obviously I haven't attempted to go through the whole dictionary so there are probably plenty of amusing mistranslations. One I just noticed was "Hop, skip and jump" is translated as "Saltar, saltar y saltar". But the big majority of the dictionary translations seem to me to be quite readable and useful.
So this opens the door for further language versions. If anyone volunteers to translate the interface, Google, with a bit of help, can take care of the dictionary. Anyone interested in this please let me know!