tContact allows you to make the site-wide contact form fully translated on multilingual sites. Categories can be set to display only in a specific language, or they can be language neutral. Depends on the core "contact" module for the site wide contact form.
Simply install the module. Then head to the Contact form settings, and modify the contact categories. Each category can be set to be shown in either a single language or in all languages (language neutral).
You can also select a category to be the default selection for that specific language, having a different default per language. The language neutral categories can also have a default selection, which will be used if no language specific category is marked as default.
To enable translation of the "Additional Information" text (Contact Form Settings), add the following line to your site's settings.php file (requires Internationalization). This is beyond the scope of this module and will not be added to the module:
$conf['i18n_variables'] = 'contact_form_information';
If you use the Contact Forms module, add the following line as well to make the "Default Additional Information for the individual contact pages" setting translatable:
$conf['i18n_variables'] = 'contactforms_information';
You can now enter a translated text in all available languages by configuring the setting with each available language selected - you must save the setting for the default language once as well. For more information, see http://drupal.org/node/313272 (Drupal 6).
The HEAD branch of this module is now for Drupal 7. This version should work, but is mostly untested.
To make the related contact form variables multilingual in Drupal 7, see the i18n handbook: http://drupal.org/node/1113374
A suitable alternative may be the Internationalization project. This has a module to translate the contact form's names and auto-reply messages (but not recipients). Extra descriptions can be translated by translating the blocks that contain those texts.