Is it possible to display the axis labels on a xmgrace plot as 0.5 instead of 0,5, which is what I get by default? Thank you!
Yes, it is possible. You need to set your machine's locale so that it uses the right decimal separator. From the command line just use
LC_ALL=C xmgrace
or set up an alias.
Have a look at the answers to this question for more details.