13. The unit as recited in claim 12 wherein said peripheral unit is initially interpreting said second control language instead of said first control language, said unit comprising: means responsive to a next command not being an end of job marker, but being an escape character, and further responsive to the peripheral unit operating in other than a binary mode of communication, to pass said command and following data to said parse means for determining whether a language boundary has been encountered.
13. The unit as recited in claim 12 wherein said peripheral unit is initially interpreting said second control language instead of said first control language, said unit comprising: means responsive to a next command not being an end of job marker, but being an escape character, and further responsive to the peripheral unit operating in other than a binary mode of communication, to pass said command and following data to said parse means for determining whether a language boundary has been encountered. 14. The unit as recited in claim 13 wherein said parser means identifies language keys for said first and second control languages and assigns each identified key a weight, said weights being summed for each control language to determine if a predetermined key threshold has been reached, said key threshold indicating the occurrence of a said language.