How to activate the French language in the back en

Hello,
How to activate the French language in the back end and in the front end?
The language files are installed correctly. If I go in "translation" translations are present. I do not understand how to activate the French language.
thank you for helping me

I rectify because the front-end is well translated. It remains the back-end

Hi

The system only show the backend in French if you login to administrator area of your site in French language. Are all other sections in the backend displayed in right French language? If Yes, then maybe the language file was broken somehow, please submit a support ticket sending us super admin account of your site so that our developer can check it

Tuan

Hello,
Thank you very much Tuan, that was it. I was connected with the default English language.