The technological advances of the third-millennium society, that of information and knowledge, in addition to the political, military, social and economic upheavals ushering in a new era whose slogans are an unprecedented brewing, mixture, and intertwining of populations in of the mankind history. This brewing and its corollary «languages contact» lead to so moving and dynamic contexts at which sociolinguists must take a fresh look at the complex multilingualism phenomena that result. While it is obvious that the concepts of "bilingualism" and «diglossia» are fundamental in the analysis of situations bringing together several languages, it is none the less true that they are struck by a certain epistemological inertia and do no longer allow more effective analysis of such contexts becoming more complex. Claiming that the two concepts («bilingualism» and «diglossia») are obsolete, we think we can revisit them in the hope of stimulating a new scientific, human and realistic debate that is more respectful of social and linguistic complexity. The results of this research should be conducive to highlight a common language contributing to the construction of unifying theories of translators, sociolinguists and many other researchers interested in transdisciplinarity. In conclusion, we tried to remove the ambiguity surrounding «bilingualism» and «diglossia», leading coin a new term («biglossia») while proposing new definitions of the three concepts which are now subject to the appreciation of our peers.