Why is "Rosen Plevneliev" pronounced with a /z/?

As I have told you in my previous question, I have heard the CBS news about the Bulgarian president visiting the US here. I don't know why, but the way the reporter has pronounced his name makes me smile. I know that that isn't an issue since we speak different languages, but I was wondering why she pronounced it that way. His name is Rosen Plevneliev. In Bulgarian there are duplicate consonants like s in sauce and z in zebra. In Bulgarian we pronounce it with clear s sound while this reporter has used the z sound.

My question is: What is the rule in English that makes her pronounces it that way.

It seems "Rosen" has been transliterated from Cyrillic characters. If the transliterator wanted the other sound, maybe he should have used "Rossen" instead. Or, as choster suggests, "Rocen". Depending on what vowel sound is desired.

Consider these English words:

rosin, rose (the flower), rose (past tense of rise), prose, chosen, lederhosen

and these names, which may not be of English origin but are familiar to English speakers:

Ambrose, Montrose, Rosenkrantz, Bose

The are all pronounced with a 'z'. I can't think of any more off the top of my head, but on the other hand I can't think of any word or name spelled with 'ose' which is pronounced with an 's'. There is no explicit written rule that one could cite, but clearly in English "ose" is predominantly pronounced with a 'z'. As to why it is so, that's just the way English developed.

And it doesn't matter if the word is unfamiliar or foreign, it's only natural that one reads a word according to the rules of the language one is familiar with. Unless the news anchor was informed specifically that the name is pronounced with an 's' and failed to do so, I can't find fault.

Also, I was impressed that they were able to pronounce his last name phonetically instead of lazily mangling it into something like "Plevenev"!

He's getting close. Now close the door.

Did you see what happened there? The first close is pronounces with the soft s; the latter is pronounced with the sound of a z.

Sure, those are actually two words – the former being an adjective meaning nearby, the latter being a verb that means to shut. But this demonstrates that, in English, even when two words are spelled exactly the same, the way an s is pronounced can change.

The only "rule" is that a s can sound like an s or a z, although I believe double-s is almost invariably pronounced with the s sound.

It can indeed be rather confusing; that's why cats asking for cheeseburgers tend to use far too many z's.

Unfortunately, trying to find consistent rules for English pronunciation is like trying to nail jello to a wall. If I had to guess, I would imagine that the reporter chose her pronunciation based on the identical transliteration of the first name to the common last name Rosen, which is usually pronounced with a voiced consonant ('z' sound) in English. This itself probably comes from the similarity to the word rose, which (I believe) owes its pronunciation to French.

Also note that the second reporter is named Roseanne, also pronounced with a 'z' sound, so there was certainly plenty of influence on the first (offending) reporter's pronunciation.