AjaxFileUpload customize language

Hi

I am using AjaxFileUpload on a Website which works great.
I would like to replace all english labels by german labels. I already tried this workaround:

http://stackoverflow.com/questions/24687983/changing-ajaxfileupload-controls-language/24688766#24688766

But it is not possible to replace all labels.
I know the translation for german is not made (found this file Resources_de.js ) so I set my webpage culture to french and tested with the french version. But while the wizard buttons changed to french the FileUpload labels stayed english.

I have no idea which files to put where to get languages other than english. Or do I have to create new dlls?
Is there somewhere a step by step manual how to put all that together and make it work?

Thanks for any help.

chris