A security measure for alien languages and encryption. It is most commonly referred to as Translation Protection.
Through means unknown to most civilization/individuals, certain pieces of data, and written words can be protected from Translation Algorithm, leaving their meaning unknown to all but natural speakers of the language.
The main method for this, is to hide a second language within the first, which would translate to a program which would stop the translation program and then self delete.
Interestingly there are means of audible translation protection.