Introduction - If you have any usage issues, please Google them yourself
A language monitor provides full duplex communication between the print spooler and bidirectional printers that are capable of providing software-accessible status information. The language monitor adds printer control information, such as commands defined by a printer job language, to the data stream.
PJLMon.dll supports Printer Job Language (PJL) and provides bidirectional communication for PJL printers.