Mary is too hard to pronounce in Spanish. I try to avoid it.

I agree with putting María, since that's the traditional Mary name, even though translating names seems to have gone out of fashion.

CK's claim is completely correct, but I am more or less on Marcelo's side. Though I don't know Spanish, I feel a little uncomfortable when I try to pronounce a German or French sentence including the name Mary. It's not really difficult to pronounce, but I think "Mary" doesn't fit the rhythm (?) of the German language.

I always treat Maria and Marie as though they were Mary.
http://tatoeba.org/eng/sentences/show/2271311
I think it's absurd to post those three sentences:
トムはメアリーを愛していたが、メアリーは彼を全く愛していなかった。
トムはマリアを愛していたが、マリアは彼を全く愛していなかった。
トムはマリーを愛していたが、マリーは彼を全く愛していなかった。


Maybe it's time Tom found a next friend.
http://tatoeba.org/eng/sentences/show/2269246

Sometimes (if not always) it really does matter how we spell/transliterate names (I'm sure that given names are subjects of transliteration, not translation). Actually, Mary, Maria, Marie, Marija, Mariah, Muire, et al. are different names though they origins are the same. This scene is maybe not the best example, but it helps to feel the difference, I believe:
http://www.youtube.com/watch?v=OI7loyAIywA

Tom had many girlfriends: Mary from England, Marie from France, Maria from Italy, Mariya from Russia and maybe some others we don't know. He even had two Japanese girlfriends named Marié and Mari.

Where I work, our policy is to never translate names (we don't even translate nicknames!), but personally, with my son, I always translate his name based on what language I'm speaking with him.

On this site, since none of these people are real, I think the policy should be to ALWAYS translate names (if a translation exists as a name in the target language, of course). People use Tatoeba to learn languages, and names are a big part of language, and I think the names should reflect that. For example, in most of the Latin sentences I've read, Tom has usually been translated as Didymus. I think that's so much more helpful than reading "Tom".

>> I think the policy should be to ALWAYS translate names
> The problem with this is that is unnecessarily generates a lot of "near duplicates."

This is not the only problem we can encounter. How should we translate a name? Should we translate it by its meaning (i.e. find a name in a foreign language with the same or similar meaning), should we replace it with the foreign analogue of the same origin or should we just find a name with the closest sounding? The 1st and the 2nd are not always possible, I believe, and the 3rd is not a translation but an adaptation (the 2nd is rather an adaptation, too).
A little example (and not the worst case, I'd said) with the name of some hypothetical person who, by pure accident, is my namesake named Дмитрий (IPA: [dˈmʲitrʲij]). Though this name is considered traditional Russian name, it's actually not since it goes back to Demeter, the name of the Greek goddess of the harvest and the fertility. The name's meaning is something like "devoted to Demeter".
We'll have no problems "translating" this name into European languages that have a good deal in common in linguistic, cultural and historic aspects. English - Demetrius, Spanish - Dmitrio, Italian - Demetrio, French - Dimitri, etc.
But what about, say, Japanese that has a bit less than nothing in common with European languages? Should it be 穣 (Minoru / Yutaka ~ rich harvest)? Or should we use ateji to make a brand new (and, probably, meaningless) Japanese name?
For me, transliteration is the most universal and simple way. One of the cases when the name translation looks reasonable is the case when the name's meaning characterizes a person bearing this name in some particular way. Another case is when a name is a placeholder name such as John/Jane Doe ( https://en.wikipedia.org/wiki/P...rent_languages ).