[Cerrado] For the users to chang the language

Background of the issue:
I am trying to change the language on my website by clicking on the flags. The issue can be seen on this page: enlace oculto.

Symptoms:
When I click on the flags to change the language, nothing happens. At best, it works just once, then not at all.

Questions:
Why does the language change not work consistently when clicking on the flags?
What could cause the language switch to fail after working once?