I have many websites, each with multiple languages using domain language selection, working with SSO. The SSO clients work fine at least (though not before making a change similar to that mentioned in issue #595020). The SSO controller site does not share sessions between languages.

Example:

Site #1 (configured as SSO controller)
http://mysite.com/ <= english
http://monsite.com/ <= french

Site #2 (configured as SSO client)
http://anothersite.com <= english
http://autresite.com <= french

Site #2 uses http://mysite.com as the controller URL. Both language domains for site #2 find the shared session, as expected. The french domain for site #1 does not however.