Hi RimHajri,
Please read the localization section in the documentation.
Check out this useful links.
https://wordpress.org/plugins/loco-translate/#installation
http://www.pixelwars.org/forums/topic/change-language-from-the-buttons-etc/
You can try these plugins;
https://wordpress.org/plugins/language-bar-flags/
https://wordpress.org/plugins/wpml-to-multilingualpress/
Thanks