Incorrect links in explicitly localized documentation

[Hans Aikema]

When explicitly browsing to a specific-language version of the userguides the
internal links link to the 'browser preferred language' version of the Userguide
rather than the currently displayed version

E.g. when browsing to 
http://lilypond.org/doc/v2.14/Documentation/learning/index.nl.html
with an 'accepted languages most significant preference for English' language
settings in the browser the displayed page is in Dutch, but all followed links
lead to the English version of the documentation.

One would expect that if a given page is in Dutch and the link-texts are in
Dutch than the linked pages will also appear in Dutch.

Allthough only a minor issue (can be resolved by modifying a browser's preferred
language sequence), it's still quite an annoyance when one surfs by default
using English (because of the many poorly translated sites one wants to avoid)
but with a google search arrives at the Dutch documentation pages to then be
presented only links for English-language versions of the Documentation pages.