I decided to try again how to handle UTF8 strings on AmigaOS4. Utility library has had functions to convert strings between UTF8 and UCS4 a little while. I was wondering always what's the use for this type of conversions. I realized that UCS4 is compatible with ASCII (ISO-8859-15 on my system).
Of course you can have your most used subroutines in one gui, say CommonRoutines.gc
and from other gui's address them as G
Gosub CommonRoutines.gc MymostusedRoutine