Ok, the language en-GB is not in the rsgallery2.XML when you install, instead is replace by en-US. Replace the two en-US to en-GB in rsgallery2.XML. Remove rgallery and reinstall it, edit the text "User galleries are disabled by administrator." to "Please register in order to create a gallery." in the file en-GB.com_rsgallery2.ini

I guess there is other way to do it, but that work for me. but all gallery is lost. You can try FTP edited rsgallery2.XML and en-GB.com_rsgallery2.ini