I have a website with Domain Access, Domain Locale and the default language is Spanish, second language is English. The detection is done by suffix ( www.example.com/es , www.example.com/en ) and the browser detection is second one. It works perfectly, in internet browsers with spanish as default language, when typping www.example.com , I will access the Spanish version. When the primary language of the browser is English, I will access the english version.
The problem arises when activating cache for anonymous users in Performance section of Admin.
I clear browser cache, and when typping www.example.com, I will be redirected to english version, with the suffix /en added to the url.
When switching off the cache, it works as expected.
I tried to replicate with a fresh Drupal installation, and cannot achieve it, so the problem is persistent only to my installation.