If the languages work in every other way except for the verification, the problem is with the IBT setup. The following is from:
http://apcentral.collegeboard.com/apc/public/repository/ap07_techtips_ap_ibt.pdf
8. Regional Settings/Options: iBT requires that all computers’ Regional Options/Settings and Keyboard Input Locale are configured for US English. The software checks for these settings before launching. Please ensure that Regional Options/Settings for US English are installed and that the default keyboard locale is set to US English.
9. Non-US English computer names: DO NOT use non-US English characters for computer names.
If the languages aren't working elsewhere on the machine, verify the language installation procedure:
Windows XP
http://newton.uor.edu/Departments%26Programs/AsianStudiesDept/Language/asianlanguageinstallation_XP.html
Windows VISTA:
http://newton.uor.edu/Departments%26Programs/AsianStudiesDept/Language/vista.html