Wrong language selection

[PeterChain]

I'm running a multilanguage database, Spanish, German, English sorted this way in the admin, and Spanish default.

 

The problem is that in an unpredictive way sometimes menu loads in english when the browser is set to spanish. This happens under internet Explorer, Firefox and Safari.

 

The problem happens under both default osCommerce menu and Coolmenu.

 

I may start a correct session in firefox, and opening a link of a product or category in a new window becomes a wrong language session, or not, I really don't understand what forces this behavior.

 

any clue ?