I am not sure what this is, it worked on rc3. Tried with Slovenian langpack on OSX 10.11.5. Please, test, this is a stopper, if it is true.
The main en-US version installs fine and works, if run. The lang-pack install however says it is not a valid install and does not want to install the lang-pack.
Tried it again and now it works. Strange. Will close as worksforme for the time being.