WPML is not free and it makes too many extra sql queries to database so it is not good solution for my site.
qTranslate saves all languages in one database row and it is very complicated to move to another multi-language plugin later.
<?php _e( '<!--:en-->english text<!--:--><!--:de-->german text<!--:-->' ); ?>
xLanguage hasn't been updated in over 2 years.
Good idea to install WordPress as multisite and each language will have its own site.