In private CultureInfo (int culture, bool useUserOverride, bool read_only) if the int culture parameter is not supported, then the message that gets logged is something like:
Culture ID 4155 (0x4155) is not a supported culture.
while this should have been:
Culture ID 4155 (0x103B) is not a supported culture.
This is caused by a regression introduced with eeeab3446fc26969d3ee639f2ca2ce670bffd71c
I found this while trying to deserialize a CultureInfo on Linux/Mono when that CultureInfo was (binary) serialized on Windows/Microsoft.Net.
Fixed in master