Cultureinfo numInfo is not NonSerialized on DotNet for windows, so it also should not on mono.
http://referencesource.microsoft.com/#mscorlib/system/globalization/cultureinfo.cs,76
[NonSerialized]
int default_calendar_type;
bool m_useUserOverride;
[NonSerialized]
int default_calendar_type;
bool m_useUserOverride;
internal volatile NumberFormatInfo numInfo;
internal volatile DateTimeFormatInfo dateTimeInfo;
volatile TextInfo textInfo;
internal volatile NumberFormatInfo numInfo;
internal volatile DateTimeFormatInfo dateTimeInfo;
volatile TextInfo textInfo;