Monarch names: english or original language?

Hello. I have a question regarding the names of the monarchs during the Spanish Empire.

For example, take a look at this image:

There you can see two different names for Charles IV; the English name, and the original name (in Spanish, Carlos IV).

So, how should these names be represented, in English or in their original language?
 

Thanks,

Piero

 It will be on the English part of this site, so the title should be English. 

Yes further down the page in the lettering section put what it says on the coin. 

See what other members think. 

I think the title should be what is written on the coin, and then it should be translated into English, that is to say the opposite of what it is today.

Please notice that the coins are still nominated “Real”, lucky enough, and not “Pound”!

Edit some minutes later:

My opinion is only valid if the things written on the coin are in our common European alphabet!

It disturbs me, that Ludwig is translated into Louis, I really don't like translating of personal names, Petrus, Pierre, Pedro, Peter etc.

I've glanced over the catalogue guidelines and I couldn't find anything. I prefer native language, but I guess it's just whatever the referee's preference is? Looking at Carlos III he's listed as Charles III on his own page, then Carlos for all issuers except for Bolivia (Charles) and the Italian ones (Carlo). 

English in the title, local language is in brackets in the feature box. 

Monarchs don't really use personal names and their royal names were nearly always translated, this has only changed since around WWII.
Personally the unnecessary pluralisation of currencies which often are uncountable in the case of denomination irks me more.

The monarchs' names should be in the original language - unless they were better known by their name(s) in English.

Aidan.

Nobody appears to ever agree on this, but from the guidelines:

4.1 English spelling

All proper names must use the form commonly used in English texts. In the absence of an obvious consensus on the spelling of a proper name, the referee chooses a form consistent with the main available references (for example Wikipedia or Encyclopedia Britannica).

✓ Robert II  ||  Cologne  ||   Juan Carlos I
✗ Roberto II   ||  Köln  ||  John Charles I