Fix language codes, add them to layout and fix Spanish

I've simplified the language codes for `fr` and `es`

> The golden rule when creating language tags is to keep the tag as short as possible. Avoid region, script or other subtags except where they add useful distinguishing information.
> http://www.w3.org/International/articles/language-tags/

Furthermore I've inserted the language code into the page's `lang` and `xml:lang` attributes and fixed a problem with the Spanish page (there was an unescaped colon).