Depends entirely on the culture. The Romans adapted other people's names into Latin all the time, and since Valyrian is modeled on Latin, it makes every sense for names to be.
And I think we even have examples from the books. Consider Kraznys, which seems pretty clearly to be a Ghiscari root that has been given a Valyrian ending (in DJP's Ghiscari, krazi means "mighty.")
And while David himself often says that names shouldn't be translated, l think he is on the right track to equate the name Jonos (Braken, Frey, etc.) to Jon (Snow). Therefore we can totally say that Ionos is the High Valyrian equivalent to Jon.
I kind of imagine it that George RR Martin did a similar process to Tolkien, whereby he translated the actual names of characters to make the names easier for English speakers. So, like how Maura Labingi is translate to Frodo Baggins, the names of characters that are named Iōnos (or the Westerosi equivalent of the name) are "translated" to Jon.
From English to Spanish, (and viceversa): John - Juan William - Guillermo Charles - Carlos Cristopher - Cristóbal Willhemina - Guillermina Ferdinand - Fernando Henry - Enrique Louis - Luis And many more that don't come to mind
A lot of names are also translated. Take the name "Christian" and its phonetic and orthgraphic variations across languages, for example. But I am also happy to see people struggling to pronounce my mother's name "Gertrud" in its proper Bavarian manner.
Names like Christian, John, William, Charles, Louis, etc. showing up in different languages with phonetic and orthographic variations is not an example of translation. It is an example of the name being very old and staying with populations of people even as their languages evolve and diverge.
It shouldn't be translated, but sometimes there are differences in the pronunciation. For example, in hebrew you would say Rivka while in english you would say Rebecca. David wold be pronounced 'Da.vid' in hebrew and 'Dae.vid' in (every?) other latin language.
In any case, I think people like to be called by they're native language's pronunciation.
Well, in the World of Ice and Fire there is the name Gregor, as in Gregor "The Mountain" Clegane. The name seems to be Westerosi and I don't think (but don't know for certain) that GRRM does not intend it to be of Valyrian origin (as some Westerosi names do appear to be.)
That being the case, Gregor/Gregori, declined like buzdar(i) seems most likely.
But if you spell it with a y (and, technically, pronounce it with a [y]), it COULD be a Valyrian name!
I believe that the name is translated to Jon in order to be more familiar to English speakers. No one in Westeros or Essos is actually named Jon, but probably Martin thought it would be preferable to change the name to something reflecting an English name rather than have his books filled with high fantasy names that people would find difficult to pronounce. An exception would be the Targaryens, whose names (Daenerys, Viserys, Aerys, etc) remain untranslated in order to reflect their Valyrian heritage.
The point of Scapeplan is not unprecedented, as he has stated in other comment, Tolkien did so before.
Also, you could see that we do so always with old biblical or classical names: Marc Anthony instead of Marcus Antonius, Aristotle instead of Aristoteles, Moses instead of Moshe, and the name of most kings throughout european history.
Or the same name John, which originally was Yohanan.
So does that mean that all names can be translated in High Valyrian or just simple ones???
It means that George R. R. Martin and/or David J. Peterson created (whether deliberately or by chance) a small handful of names that sound similar enough to European names that they declared them functionally equivalent.
So no, not all names, but neither is it a matter of "simple".