~$ locale
< ... all set to hu_HU.UTF-8 ... >

[001] ~$ perl -e 'printf(q{%f}, 123.456);'
123.456000

[002] ~$ perl -e 'use locale; printf(q{%f}, 123.456);'
123.456000

[003] ~$ perl -e 'use locale; use POSIX; POSIX::setlocale("LC_ALL", "hu_HU.UTF-8"); printf q{%f}, 123.456;'
123.456000

[004] ~$ perl -e 'use Gtk2 -init; printf(q{%f}, 123.456);'
123,456000

##</code><code>##

[005] ~$ perl -e 'use Gtk2 -init; print unpack("H*", 123.789) . "\n";'
3132332c373839

[006] ~$ perl -e 'use locale; print unpack("H*", 123.789) . "\n";' 
3132332e373839

[007] ~$ perl -e 'print unpack("H*", 123.789) . "\n";' 
3132332e373839

[008] ~$ perl -e 'use Gtk2 -init; print unpack("H*", "123.789") . "\n";'
3132332e373839

[009] ~$ perl -e 'use Gtk2 -init; print unpack("H*", 123.789 . "") . "\n";'
3132332c373839