Hi Marc!
Indeed, constants look like the best choice, apart from the fact that translators will have to adapt.
We could even create a simple PHP script that turns variables to constants. We could run that to turn old style translations into new files...
But I think it wouldn't make a change for translators. Especially if we adapt to the proposed Online translation system, from Michal... (to which I'm +1, but I think not much people might use it?)
Regards, Garvin