You can search for articles in different luxembourgian newspapers:
http://www.eluxemburgensia.luI did a quick search but the only thing I found, was the obituary of Katharina Weicherding, she was the widow of Nikolaus Meis and died June 4, 1944.
One of the bereaved in the article is a Johann Joly-Meis, I think this you could be your Jean Joly.
Especially because Nikolaus Meis and Katharina Weicherding had a daughter, Marie born December 1, 1909.
http://www.eluxemburgensia.lu/BnlViewer/view/index.html?lang...https://familysearch.org/pal:/MM9.3.1/TH-1942-32040-9525-73?...You can also contact the municipal administration of Diekirch:
http://www.diekirch.lu/fr/contact/