Oscar is multi-lingual. You just need to change the language in your browser and Oscar will switch to that language.
Note: Each language has a file containing text for that language. For Oscar 12 in french, the file is:
/var/lib/tomcat6/webapps/Oscar12_1/WEB-INF/classes/oscarResources_fr.properties
Currently 5 files exist:
en (English), es (Spanish), fr (French), pl (Polish) and pt_BR (Brazilian Portugese).