09:12 Sep 29, 2011 

Thanks to everyone for your input and suggestions. The detailed points made by Charles in the discussion were particularly useful. It's one of those cases where it's hard to assign the points to one particular person. I guess I'll have to give them to the answer that proposes (or confirms) the format I actually ended up using in this particular case.

04:05 Sep 28, 2011 

Thanks for taking the time to give that very thourough answer, Charles. My text is something like an exhibition catalogue, so translated title + date in parentheses looks like the best option in this case.

22:17 Sep 27, 2011 

To clarify: if the text is a formal piece of academic research, the house style of the publisher or journal must be used, and this, by default, will tend to be MLA rules for the US (see Pablo Julián's answer) and MHRS (whose style guide is silent on this point) for the UK. Square brackets would certainly be appropriate in this context.
On the other hand, for books and essays of a less formally academic kind, or for exhibition catalogues, for example, putting the date after the translated title within the same parentheses is quite normal.
Of course this question only arises when both an original and a translated English title are given, and when translating from Spanish into English this will normally only happen with Spanish works, and not always then. Some titles, such as Las Meninas, will not be translated at all, by convention. When the Spanish source text refers to a non-Spanish work under a translated Spanish title (as often happens), it obviously makes no sense to retain this in the English version; just an English title will normally be sufficient. And of course if there is only one title it just goes in italic and the date follows in parentheses.

16:22 Sep 27, 2011 

The rule is whatever the client/editor says it is, but my default practice nowadays, unless they've told me otherwise, is Original title (Translated title, Date): i.e. as in your first example. If it's for someone I haven't worked with before I draw attention to this in a note. Some clients give you a style sheet; otherwise, where possible, I ask in advance and/or try to look at their previous publications. Jenni is absolutely right that often only the translated title is used. And I have also seen Pablo's style, using square brackets, quite often. It's best to clear this up with the client in advance if you can, because it's always risky leaving it up to them to change the presentation of titles to their desired style; deadlines are often short and things get missed.

15:52 Sep 27, 2011 

In answer to your question, again it's a matter of style, but many of the art books and catalogues that I own use either the English title or the best known title (italicized) in the body of the text. For example, on page 465 of my copy of Janson's History of Art, only the English titles of works by Parmigiano are used, both in the text and reproduction captions. However, in the "New Painting" catalog mentioned in my entry below, only original titles are given in the body of the text and translations are provided in the captions of the illustrations. These are style sheet items that should be worked out with the writer, editor or publisher. In any case, once established, the same rule should applied throughout the document.

15:39 Sep 27, 2011 

Just to clarify, I'm interested in the best approach to use when this appears in the main body of the text (not in the foonotes or bibliography).

14:10 Sep 27, 2011 

Perdón, con Mercedes!!!! ;)

14:09 Sep 27, 2011 

estoy de acuerdo con Ross

14:08 Sep 27, 2011 

Yo diría la primera. Saludos. Marta.