A Chinese version of the Release Preview (build 8400) has appeared on the internet.
The ISO is named 8400.0.WINMAIN_WIN8RC.120518-1423_X64FRE_CLIENT_ZH-CN-HRC_CCSA_X64FRE_ZH-CN_DV5.ISO, and the build was compiled on the 18th of May at build 8400.
The build was available for download on non official Microsoft servers but was yanked relatively soon after that.
It’s pretty obvious that the heat from Microsoft must have come down really hard on the leak source.
The official version of this build is expected to launch within the next couple of weeks as well as the English version of the Windows 8 Release Preview.