The URL language provider configuration form.
function locale_language_providers_url_form($form, &$form_state) {
$form['locale_language_negotiation_url_part'] = array(
'#title' => t('Part of the URL that determines language'),
'#type' => 'radios',
'#options' => array(
LOCALE_LANGUAGE_NEGOTIATION_URL_PREFIX => t('Path prefix'),
LOCALE_LANGUAGE_NEGOTIATION_URL_DOMAIN => t('Domain'),
),
'#default_value' => variable_get('locale_language_negotiation_url_part', LOCALE_LANGUAGE_NEGOTIATION_URL_PREFIX),
'#description' => t('<em>Path prefix</em>: URLs like http://example.com/de/contact set language to German (de). <em>Domain</em>: URLs like http://de.example.com/contact set the language to German. <strong>Warning: Changing this setting may break incoming URLs. Use with caution on a production site.</strong>'),
);
$form_state['redirect'] = 'admin/config/regional/language/configure';
return system_settings_form($form);
}