Hi,

please update documentation on the module webpage to describe configuration of 7.x version.
Here is sample text:

To use this module, you should set URL method in admin/config/regional/language/configure and configure each language. For example, if you use "path prefix" method at admin/config/regional/language/configure/url you should enter prefixes in configuration of each language in admin/config/regional/language ("Path prefix language code").

You must set URL as the most important language selection option in "User interface text language detection". This option is located at admin/config/regional/language/configure . You must simply drag URL to the top of list.