I often work on multilingual websites. I fully internationalized the php files of the plugin and translated the admin to French (have a version available for you, if you want ^^)
Nevertheless, there is a small problem with the fact that templates are htm / html files only. Therefore, it is impossible to add any php code inside (I’m on a shared server where the addtype command in .htaccess is not activated, because of CGI)
So would it be possible to have templates with .php extension ? It is actually possible to create a different template for each language, but I find this is a bad practice.