Windows has code page and UTF-8 redefinitions for du macro.
How about Linux.

Do you mean to ask what code pages does the Linux console support? Because the du macros in the Windows download can still be used in Linux assuming that Linux uses the same code page sets.

I'm not (yet) a Linux user, but it seems that Linux uses UTF-8 instead of code pages. If Linux only uses Unicode then FASM would have to use UTF-8. However, the UTF8.INC macro is not in the FASM Linux package.

I think the main purpose of the du macros is to convert source code in one code page (which could be UTF-8 or CP1250 or whatever) into Unicode (UCS-2 or UTF-16). But if Linux doesn't support UCS-2 or UTF-16 then du is not going to be helpful to you.