Thanks. This is not a problem with automatic language selection, which
works as intended. The problem is that once in a translated page, we
should make links on it to point to translated pages as well.
For example, you are in notation/rhythms and auto language shows you
the English page. You switch to German and want to go to 'beams'. The
link to 'beams' in German page should point to notation/beams.de.html
so that you stay in German pages. Instead, it points to notation/beams
which shows the English page again.