I18N.dll and I18N.CJK.dll don't work with IL2CPP

My project works fine in mono2x (stripping assemblies) but in IL2CPP.

It will show

ArgumentException: Encoding name ‘BIG5’ not supported
Parameter name: name
at System.Security.Principal.WindowsIdentity.System.Runtime.Serialization.ISerializable.GetObjectData (System.Runtime.Serialization.SerializationInfo info, StreamingContext context) [0x00000] in :0
at System.Text.Encoding.GetEncoding (System.String name) [0x00000] in :0
at BBS.TelnetConnection.CovertToString (System.Byte datas) [0x00000] in :0
at BBS.TelnetConnection.StoreText (System.Collections.Generic.List`1 datas) [0x00000] in :0
at BBS.TelnetConnection.Update () [0x00000] in :0

(Filename: currently not available on il2cpp Line: -1)

I find a similar question in past post

Is it still a bug in unity 5.2.1f1?
How do I fix it?

We had a bug with I18N.dll and similar assemblies which is corrected in 5.2.1p2 and later. Please give that patch release a try, and this should work. You can find the patch releases here: