At the present time ElumTools doesn’t have any language localization built in (everything in the program is in English, by default). However, some possibilities do exist to translate the output.
ElumTools stores most of its output as Shared Parameters on the ElumTools Calculation Points Family. There isn’t currently a good mechanism to rename the shared parameters, to be in another language. However, we may be able to add that functionality to the program in a future update.
The main way to report results in ElumTools is to create a schedule. Revit schedules allow you to rename the fields, so you could create a schedule and then translate to another language. See below. So that may help you accomplish what you need, for now.