When do you translate a name?

This morning, I was listening to the morning 24horas broadcast, and listened to the story about the 90th birthday of Reina Isabel (Queen Elisabeth). The next story was about a book fair where people could buy books from great authors, including William Shakespeare.

Waitasec... Why translate "Elizabeth" into "Isabel" but not "William" into "Guillermo"?

I already knew that European explorers during the "Age of Discovery" were all given transliterations into various languages, with "Christopher Columbus" being known as "Cristóbal Colón" in Spanish and "Christoph Kolumbus" in German; "Amerigo Vespucci" is known as "Américo Vespúcio" in Portuguese and Spanish; and "Ferdinand Magellan" is known as "Fernando de Magallanes" in Spanish and "Ferdinando Magellano" in Italian. True, the differences were not often great, but many of the "great European explorers" of that era are known by their transliterated names (so if a German typed "Christoph Kolumbus" into the Spanish-language Wikipedia, they don't get to the "Crist{obal Colón" page).

But what about authors and monarchs?

I went to look at the Spanish-language Wikipedia page for William Shakespeare, and it is: William Shakespeare. There is no other moniker by which he is referenced on the Wikipedia page (which I use as my easy-access translator). And so I went a little further, and checked other Latin-script alphabets, and they all called him "William Shakespeare." Even in Gaelic and Hungarian, the spelling remained the same, despite their highly distinct orthography. But the entry on Queen Elizabeth II all had the name and title always translated into the linguistic equivalents.

Okay, so what about other famous English-named authors?

• James Joyce is always spelled JAMES JOYCE in all Latin-script Wikipedia pages.
• Mark Twain is always spelled MARK TWAIN (and his real name is always spelled SAMUEL LONGHORN CLEMENS) in all Lantin-script Wikipedia pages.
• Jane Austen is always spelled JANE AUSTEN

What about Classical-era authors and philosophers?

• Homer is transliterated into different versions (e.g., Homero, Gomer)
• Pliny the Elder (Gaius Plinius Secundus) is translated into different versions (e.g., Plinio el Viejo, Idősebb Plinius)
• Aristotle (which is transliterated from the Greek Ἀριστοτέλης) is transliterated into different versions (e.g., Arastotail, Arystoteles)

So it seems that famous English authors retain their names (at least since Shakespeare forward), but names from the Roman Empire and before got transliterated (and translated when there were descriptors associated with that name). What about monarchs?

• William I (aka William the Conqueror) has his name translated into the native version in all cases.
• Charles I of Sweden is translated from the Swedish Karl I, and it is subsequently translated into the local variants of Charles/Karl.
• Stephen I of Hungary is translated from the Hungarian Istvan I, and it, too, is translated into the local variants of Stephen/Istvan.
• Al-Mansur of the Persian Abbasid Caliphate is known as homonymous versions of either "Al-Mansur" or "Abu Ja'far" in all Latin-script Wikipedia pages.
• Ibrahim I of the Ottoman Empire is known by homonymous verions of "Ibrahim" (not "Abraham") in all Latin-script Wikipedia pages.

So European monarchs have their names translated, while non-European monarchs apparently don't, even when the name exists within a European context, such as with Ibrahim I. But then what about non-monarchical heads of state?

• Thomas Jefferson remains spelled THOMAS JEFFERSON, despite there being transliterations of Thomas in other European languages.
• George Washington remains spelled GEORGE WASHINGTON, despite there being transliterations of George in other European languages.
• Oliver Cromwell remains spelled OLIVER CROMWELL, even though there are many different versions of Oliver across Europe.

So, monarchs have their names translated. Non-monarchical heads of state don't have their names translated. Interestingly, when I looked up non-monarchical heads of state on the Russian pages, their names were transliterated from the pronunciation in the original language, so "Charles de Gaulle" was transliterated to "Sharl de Goll," which is far closer to the French pronunciation than if they had used the same transliteration that they did with Charles Darwin ("Charlz Darvin").

I guess the rules for translating names of people (between European languages) are:

1. If it is a European monarch, you translate the name to the local language equivalent.
2. If it is a Classical anyone famous, you transliterate and/or translate the name to the local language equivalent.
3. If it is an explorer from the Age of Discovery, you translate the name to the local language equivalent.
4. If it is anyone else, you leave the spelling as-is.