This is exactly the same as version 6.11.1 but bumps the major version number to indicate the presence of a BC break in child classes. The changes in 6.11.0 and 6.11.1 have been reverted in 6.12.0. If you have code that depends on those changes, please upgrade to 7.0.0 instead. Apologies for the mix up.
Specifically, lang(), setLanguage(), and $language are now static, and should be called statically.