These are strings and they work on one language either you can translate in french or some one else not possible they change automatically.You can change all strings from our language file which you found on the following path (contra > langauges > contro.po). Open this file in po editor and change all strings like next previous buttons etc. po editor is free and you easily download it from google.
How can I translate “next post, prev post” on single project page? I will use the web site in 2 languages.