Name change/move edit

Why is this page listed under John William when his name was Johann Wilheim? It's somewhat strange that this name is Anglicized but the name of his son, for example, is given as Wilheim Henrich, instead of William Henry. Kaiser Wilhem, as another example, is Wilhem in the English Wikipedia but Guillaume with a German language tag in French. This is a weird inconsistency - I was under the impression that names did not change based on language - and might be a good subject for discussion as this would potentially apply to a number of biographical articles.