Problems with languages

My website is in french language since 1 year.

Now, we would like put English language by default.

We changed the values in SETTINGS / LANGUAGES / SETTINGS LANGUAGE

We changed the values in GENERAL SETTING  (We have put US)

No all seems Ok... However, when a visitor come on the site, the index is well in english. But after login, always in index page, the language became French

All the cache server are Ok...

My navigator are well in english language...

Have you an idea ?

Thanks per advance

I think - and I could be wrong - when you have multiple languages, dolphin determines which is the default language (by some way) and displays site in that language - provided there is a translation of this language available. So if you are on the site in France, then it should default to French, and I believe this is regardless of what you set as the default language.