Redirect to a language

Hello,

Some users told me that when they switch from one language to another, the site goes back to the first language, which is the first language of the site to their system language. This happens only in this case.

My website has been built in English then I have added French, Italian, Spanish, Russian and Ukrainian. Basically they can access all languages but when a french user select English they are redirected to the french.

Any idea? The concerned site is here: https://www.yvanhunt.com