Are the two languages appearing on the same page, or only on facing pages? What are the languages? Is one of the languages predominate in the sense of being the original language of the text or the language of the principle audience for the book (this can be the case, for example, in bilingual literary texts or scholarly editions). If the two languages are to be considered of equal importance, then you need to come up with a solution that doesn't give the impression of making one primary, e.g. by setting it in roman (regular) type and the other in italics.

{To Follow}

I forgot that, it's a photographic book, in spanish and english, the principal is the spanish. and the text is in the same page, under the image, as a description.

Find out which language sets longer (if any). If one language is longer, choose a typeface with an italic that has a greater character count per pica.

Also, try and make the layout consistent, so that when readers turn the page, they are anticipating seeing their language in “its” place. If you achieve this, it might be possible to use the same spec for both languages.

I don’t like greying type (unless with a spot color) because it kills the sharpness of the type.

Making one language grey will automatically demote it and give it second place, so it’s not something I would do, unless that was intended. Here in Canada I would never deal with French and English together that way.

For photo captions, your bits of text should be relatively short. What you need to do is keep the text in the two languages of equal visual colour, yet keep them distinct from each other. Going roman/italic is one solution. You could also go serif/sans. I wouldn’t worry about varying text lengths as you can accommodate them in your design; again, it’s the overall text colour I’d be more concerned about, so that one language doesn’t dominate the other.

Another solution would be simple placement. Put enough space between the two captions so it doesn’t look like the reader should read on from the other and keep the positions of the captions consistent in relation to the photographs. Not knowing the nature of the photos or the trim size of the book, it’s difficult to be more specific, but a left/right or top left/bottom right arrangement could work in the right design.

I've done a number of these including a three-volume trilingual series. John pretty much nailed it. As long as there is no confusion about which language you're in as you read (& that in itself would be a strange notion), why would you want to graphically say, "Boy, these languages are different"? Only if you can come up with a reason in a particular case, does the idea makes sense.

There are other problems, usually one language is not as efficient as the other, so if you're going to maintain basically the same place on the page with a side-by-side presentation, you have that problem to address. It's easier to solve if you keep one language on the verso, one on the recto. If the trim is large & two columns would work, that's an option, too. If you want the simultaneity across the page/spread really tight, set ragged.

Footnotes, if used, can be a factor. Here's an example. The poetry volume in that tri-lingual series was trouble. Basically, the languages used were indigenous, English, and Spanish The editorial decision was to have the footnotes in both English and Spanish for the indigenous language, and then English with the English & Spanish for the Spanish. As a design, it It would have been easy to just have four columns & handle things that way, but the editors decided differently (& wrongly, I felt).

In another book I did, English was so much more efficeient that we set all the footnotes on the "English" page. Depends on how many & how complex the footnotes are.

Etc.

So, I think a word in your thread title is important: editorial. The languages themselves in simultaneous presentations aren't really a graphical problem, but the layout can be greatly eased if the editors work with the designer.

FWIW

If you are able to maintain consistent positioning of the two language texts relative to the images to which they relate, I don't think you need any typographic distinction between them. The reader will quickly attune to the positioning convention, and immediately locate his or her language on each page.

If you find you do need to make a typographic distinction, consider pair serif and sans serif, since most of the text per page is presumably quite short.

the principal is the spanish.

Note that which language is the original versus which is the translation does not necessarily mean one should look more important. As David opines, that's rarely desirable.

Concerning captions, one trick would be to use them to separate the two languages (like in Lane's "The Diaspora of Armenian Printing, 1512-2012", although in that case the writing systems are different).

Find out which language sets longer

Spanish is typically ~10% longer than English, but translation is about ~15% longer than the original, so you might be lucky and end up with very comparable lengths.

BTW for comparative language lengths get a copy of "Typographia Polyglotta" by Maxim Zhukov and George Sadek. Although it's over $100 now, whereas years ago I got mine for ~$20.

try and make the layout consistent

Yes, this is key. But to me that doesn't make using identical typography (a Modernist fetish) a good idea; there is always something different about the two languages/cultures, and being sensitive to that difference does not have to result in gimmicky differentiation. It is however tricky business, which is why many people give up and pretend making them identical is a good solution.

Concerning specific suggestions:
- I think using Roman and Italic is rarely a good idea - the latter is too casual.
- Using serif and sans is also problematic: big readability difference in addition to a huge formality difference.
- You need subtlety in your solution; check out Lisboa - see the first entry here:
http://typographica.org/on-typography/our-favorite-typefaces-of-2005/
It's not a serif font, but it is suitably Iberian! :-)
- Consider using Rotis (as Aicher did in his monumental book) since it has four flavors, or Linotype's comprehensive Compatil system. Note that both of those designs are generally maligned, but I don't think they deserve that.

hhp

I finally remembered something I wanted to also mention: Whatever you do, don't emulate the dronefest in Emil Ruder's "Typography".

hhp