The official website actually uses the English "Night" in the glossary link, so I think I would prefer walpurgis_night_(madoka_magica)
Posted under General
Aliasing walpurgis_no_yoru_(madoka_magica) -> walpurgisnacht_(madoka_magica).
Reason: Walpurgisnacht is the original German name, and it's pretty clear that it's what's meant. "no yoru" is basically a direct translation to make it more accessible for the Japanese viewer.
Updated by jxh2154
The official website actually uses the English "Night" in the glossary link, so I think I would prefer walpurgis_night_(madoka_magica)