Define-Pages Content saved to wrong language files

Hi,

I have a wierd issue I cannot re-solve myself so far.

I have a zencart 1.5.1 installation with additional language pack installed. Administration panel shows up normally, but when I change the content (Tools / Define Pages Editor) - the changes are made within the includes/languages/english/html_includes/define_contact_us.php instead of includes/languages/other-language/html_includes/define_contact_us.php - and in the front-end area I cannot see the changes. It stays the same text as it was before. I only see changes if I check the file manually on the server.

Why does ZenCart keeps showing the /english/ content if the default language selected is the other one?

Because you should be using a template override for those changes to take effect.
http://www.zen-cart.com/content.php?181-the-override-system-really-simplified