Version 1.0 of SubjectsPlus is using gettext to translate strings. This is a standard way of handling internationalization, and should work much better than the previous hacky way.
There is now a French version of the beta ready, thanks to Benoit H!
Make sure there is a translation for your language
Look in sp/assets/locale/ Do you see an appropriate folder for your language? If so, check inside and see if there is a messages.mo file in there. If so, you should be good. If there is just messages.po, it hasn't been translated or compiled yet. Send a message to the google group.
Set up the translation in sp/control/includes/config.php
You will see a section in there that begins, say,
$language = 'fr_FR';
Change the language to the appropriate one.
$LocalePath = "/home/myname/www/sp/assets/locale";
set the $Localepath (the path from the root of your server to the locale file)
Uncomment the whole section if it's commented out.
NOTE: You may have to restart your server for the changes to take effect