P.S.: I saw some comment in another thread about 'localizing $_'

That was probably a reference to dynamic scoping with local() rather than localization.

P.P.S.: See also the perl.i18n mailing list and Sean Burke's article on Locale::MakeText in TPJ #13.

Before that, you pretty much have to use Unicode::String and accept the performance penalties (which are quite significant). *shrugs*

Now, Parrot-targeted languages will have Unicode built into the ASM (as it were), but I'd direct anyone interested in this to read the parrot mailing list for more info.

Yes, there has been a long running discussion on this on the perl6-internals mailing list here and here for anyone interested.

I use POSIX locales with HTML::Template or SSI for internationalization. It works pretty well. I'm sure any decent templating system would do (Template Toolkit, anyone?).

use locale;
use POSIX 'locale_h';
my $loc = "de_DE.utf-8";
setlocale(LC_CTYPE, $loc)
  or die "Invalid locale $loc";
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This code is probably from perllocale, which is another great source for this sort of thing.

BTW AM/PM is AFAIK strictly an Anglophone thing. No other language uses it. But the one that really gets you is the decimal/comma inversion on the European continent: 3,14 vs 300.000.000 EUR or 300 000 000 EUR. =)

However that's not what you asked about.

The other thing that DateTime handles is locales. For this, it has used the Common XML Locale Repository project. So, once you have your DateTime object, all you need to do is set the locale and output it with strftime. All the strftime functions are localised, so getting the month name will always return the name in the current locale. The %c token is the default date-and-time format for the locale:

use DateTime;

$dt = DateTime->now();

print $dt->set( locale => 'en' )->strftime('%c') . "\n";
# May 2, 2004 9:45:18 PM

print $dt->set( locale => 'en_AU' )->strftime('%c') . "\n";
# 02/05/2004 9:45:18 PM

print $dt->set( locale => 'es' )->strftime('%c') . "\n";
# 02-may-04 21:45:18

print $dt->set( locale => 'fr' )->strftime('%c') . "\n";
# 2 mai 04 21:45:18

print $dt->set( locale => 'it' )->strftime('%c') . "\n";
# 02/mag/04 21:45:18

print $dt->set( locale => 'no' )->strftime('%c') . "\n";
# 02.mai.04 21:45:18
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I also tend to use maketext, as there are utilities like poEdit to handle the language files.

As for your other questions:

• localizing $_ relates to scoping problems of the variable $_. It doesn't have to do anything with localization.
• I haven't seen a non-English error message from Perl so far. This is not a huge deal, as users shouldn't see Perl's messages anyway.
• if you use locale, a number of things will be adapted to the current locale. For example, in a German locale, sprintf() will format a floating point number as 1,25 instead of 1.25. strftime (from the POSIX module) will format date and time strings correctly according to the current locale (e.g. Mi 13. Januar 2004, 17:52 instead of Wed, January 13th 2004, 5:52pm. Also, the sorting order will be affected by the locale (e.g. in sort).

Go and read perllocale, it has some more interesting information. For example, you can also find out the currency symbol of the current locale so you can print ¥100 or €100 instead of $100.

One last hint: Whatever approach you use, use a format that comes with tools like poEdit or is easy to understand. The better your software is and the easier it is to translate it, the more people will volunteer to translate it to another language (talking in a open source context, not business, of course).