The menu that lets users quickly change the language of the interface is a "jump" menu, meaning it executes as soon as the value changes. This is a problem for assistive technology users because the action can execute when they are just trying to browse through the options. There are two potential solutions.
1. Us a "go" button in conjunction with the select menu. - http://oit.ncsu.edu/itaccess/forms#jump
2. Remove the menu altogether. It takes up valuable screen space and most users will never need to change the language that regularly. If they do they can change the language in their profile. As a middle-ground option there could be a setting in the user profile to allow users to choose whether or not that jump menu is present on the top of their pages. That way users who do need to frequently change languages can still do so.