Unde linux, the foreign keys such as ü Ü do not seem to work with this code:
String.fromCharCode(e.charCode).toLowerCase();
The output is wrong under Linux, but Windows is Ok.
Here is sample page to debug this: the output of foreign keys such as ü with Linux looks same here, totally broken, two chars appear: http://www.bgxcomponents.com/flashValidateRegExp.htm