IupSetGlobal("UTF8MODE",YES")
just after primary IUP toolkit initialization function:
IupOpen()
But... I was unable to get UTF8 strings working for example with IupFileDlg() function...

Also was unable to find a solution how to return string value from IupGetAttribute function.
As for positive findings - I was able to compile all libraries from source using MinGW/MinGW64 on Windows platform
to static / dynamic libraries. Looks like there is an issue using such libraries with PureBasic: if i use them - PB
could compile and create an executable file that i could run lately. But if I try to compile and run from within PureBasic
IDE it's crashing while using .dll files generated by MinGW compiler.