It's possible to have template and parameter descriptions in several languages in TemplateData, and it's possible to edit them in the TemplateData editor, and this is great.
It would be even better if the editor could show an existing description in another language. This would make it work like a translation interface.
The default language to show should probably be the content language of the wiki, if there is a description in it, but it should be possible to select another language, too.
The DOM element that shows the description in a source language must have lang and dir attributes set appropriately.