Hmm, I can't replicate that. I run gretl with LANG=de_DE.UTF-8, select
the option of using the locale decimal character, and enter two lines
of code in the script editor:

x = 13.7
eval x

* I run the script and see "13,7" on output.

* I turn off the locale decimal character, run the script again, and see "13.7".

* I turn the locale decimal character back on, run the script again,
and see "13,7".

I can replicate your behavior when I set the language explicitly to German (and restarting gretl). But I see the problem previously described when my setting is "auto" (on a German Windows installation, or rather: Windows set to German).

thanks

sven