Add language switch for wordpress users

I use a theme and plugins which support localization, and which can display feedback nformation in different languages.
I would like to enable front end users of my WP site to choose which language they want to use to browse my site, by providing a select field on each page for instance.
How can I do that?
I am not looking for localization plugin such as WPML or Polylang. I just want to know how a user can change the default language used by WP from the site itself.