I probably ought at least find out exactly what that change of behaviour is

Here's the script that demonstrates that change of behaviour:

use warnings;
use locale;

$m = "3.14e+9" + 0;
$n = "3,14e+9" + 0;

print "\$m is $m\n";
print "\$n is $n\n";
[download]

On current bleadperl (and recent "double" and "long double" perls) it outputs:

$m is 3140000000
$n is 3140000000
[download]

But when I patch bleadperl to assign with Perl_strtod (or run that script on a quadmath build of perl) it outputs:

$m is 3140000000
$n is 3
[download]

AFAICT, it pertains solely to the numification of strings. When values are assigned as barewords, there's no difference between the behaviour of the various builds.
And I think it comes into play only if the locale radix character is a comma.
My next step is to find out whether this needs to be fixed before my proposed patches can be applied.

Cheers,
Rob