Multiple Languages Question

I intend to create a version of a site in a second language. I have read around the forum enough to know that a general intro page in the second language is not enough. If I understand the intention, the user must be able to use the site in the second language.

I'd like to get a better reading on how this is applied. For example, would every page of the English-language site have to appear in the second language?

In my case, about 70% of the site would have to be reproduced in the second language for booking/understanding terms etc. However, there are areas where there are pictures. No instructions necessary, click on the thumbnail you want and you get the big version. I'd ideally like to avoid duplicating these.

TIA

The editor in the second language won't be comparing the site to the version in other languages. S/he'll look at the site in the languag s/he is reviewing it for, and evaluate that site's value for surfers. So it doesn't matter if 10%, 30% or 70% of the pages are translated, as long as the result is a functional site with sufficient content for the category.

Hope that makes sense