This might be a bit on the edge of what is suited for this sub, but it still made me wonder. This is something I notice a lot when learning about history in English after I was taught in Dutch. Examples:
King James II is called "Jacobus II" in Dutch
Willem van Oranje is called "William of Orange" in English
Karel/Karl/Carlos V is called Charles V in English.
Translating the name someone was called seems odd to me, and for some reason, we no longer do this at some point in time, with Kaiser Wilhelm being a name so familiar to people we don't even translate the word "Kaiser" any more. Why do we translate these older names, and why did we stop doing so in more recent times?
Willem van Oranje is called "William of Orange" in English
'William of Orange' in English usually refers to William III (his great grandson who became king of England), not to William the Silent. This can lead to quite a bit of misunderstanding, so it's important to know.
In earlier times it has been more acceptable to translate the names/nicknames of foreign rulers. It's not just Dutch that does it, either - look at the names of the Eastern Roman emperors in English, for example. Not all of them are localized, but in English you'd use Basil, Constantine, John, Michael etc instead of the original Greek names.
Translating proper names has been studied quite a bit and it's a pretty relevant question in translation studies, specially in the field of literary translation. There are different ways of doing it, too. For example, in this paper (which actually focuses on translating names in children's literature), the author names names conventionality as one of the possible translation strategies. In his own words:
This final procedure occurs when a TL [target language] name is conventionally accept ed as the translation of a particular SL [source language] name. It is commonly used with names of historical /literary figures and geographical locations.
If you're looking for examples, the Finnish names of any historical figures provide plenty of them. The Finns have a thing for localizing everything and it really seems like they do it more than most other people (though it's partially caused by the Finnish alphabet typically having one letter per sound). They speak of Arkhimedes, not Archimedes, and Rikhard I Leijonamieli, not Richard I Lionheart.
The same thing happens with geographical names. Languages tend to have different names for locations/nations they're more familiar with, because the names were adapted to the target language and culture. A great example would be the many names of Germans in other European languages.
I guess in modern times it's usually assumed that the recipient knows enough of the topic to recognize foreign names and associate them with the correct people/places/etc. Nowadays people tend to value accuracy over sounding nice in the target language.
Follow-up question: what exactly is the standard for translating names in academia? I've seen it done all different ways (for instance, I've definitely read published papers where Charles V is written as Carlos V, and my grad profs have never complained as long as I'm consistent. Is there a resource that outlines the conventions for this?