Language codes not implemented
Literals in the string pool are not encoded with language codes. In the past, this was put off "until later", but it is a serious lapse in supporting the RDF standards.
The places where literals are stored and retrieved from a byte buffer are:
The SPStringImpl class.
SPObjectFactoryImpl.newSPObject(Node) this converts a LiteralImpl into an SPStringImpl
I suggest using an escapable code for a separator character. This will allow minimal changes to the current system.