Now I've apache configuration which works just with localhost domain (http://localhost/).

Alias /media/ "/ścieżka/do/instalacji/django/contrib/admin/media/"
Alias /site_media/ "/ścieżka/do/plikow/site_media/"
<Location "/">
    SetHandler python-program
    PythonHandler django.core.handlers.modpython
    SetEnv DJANGO_SETTINGS_MODULE settings
    PythonPath "['/thomas/django_projects/project'] + sys.path"
    PythonDebug On
</Location>
<Location "/site_media">
SetHandler none
</Location>

How do i allow it to be employed by some subdomains like pl.localhost or united kingdom.localhost? This subdomains should display exactly the same page what domain (localhost).

Second question: It's possible change default localhost address (http://localhost/) to (http://localhost.com/) or (http://www.localhost.com/) or something like that else?

You should use the ServerAlias directive in apache for various hosts

NameVirtualHost *
<VirtualHost *>
ServerAlias pl.localhost
ServerAlias uk.localhost
Alias /media/ "/ścieżka/do/instalacji/django/contrib/admin/media/"
Alias /site_media/ "/ścieżka/do/plikow/site_media/"
<Location "/">
    SetHandler python-program
    PythonHandler django.core.handlers.modpython
    SetEnv DJANGO_SETTINGS_MODULE settings
    PythonPath "['/thomas/django_projects/project'] + sys.path"
    PythonDebug On
</Location>
<Location "/site_media">
SetHandler none
</Location>
</VirtualHost>

but when you do not use internet domain names having a set up dns you'll need and to update yor hosts file using the hosts you are attempting to make use of.

yes thanks Meska, I resolved the issue. I put into '/etc/hosts' file something similar to:

127...1 pl.localhost

127...1 united kingdom.localhost

127...1 www.localhost.com