Decimal separator and sort statement: When using the Sort statement I ran into a problem with decimal point vs. decimal comma. The users logon in German but we (SwissGermans) use decimal point, not comma. It seems that the Sort statement does not work correctly with this 'hybrid' combination.
Yes, this is true. GuiXT assumes decimal separator "comma" when you logon in German. Please use the statement Decimalseparator to tell GuiXT the decimal separator character you desire, e.g.

Decimalseparator "."

or

Decimalseparator UserDefault

See the Decimalseparator keyword documentation for details.