A podcast re: the CEFR can be found here: https://www.cambridgeenglish.org/research-and-validation/interviews/
The seminal article about communicative competence (Canale and Swain, 1980), can be found at 
https://www.researchgate.net/profile/Merrill_Swain/publication/31260438_Theoretical_Bases_of
_Communicative_Approaches_to_Second_Language_Teaching_and_Testing/
links/0c960516b1dadad753000000.pdf
A short video about testing general language proficiency: https://www.britishcouncil.org/exam/aptis/research/projects/assessment-literacy/general-language-proficiency
Defining levels of language proficiency: https://www.accreditedlanguage.com/interpreting/defining-levels-of-language-proficiency-avoids-confusion/
A brief overview of proficiency: https://languages.wisc.edu/proficiency/
ACTFL proficiency scale: https://www.languagetesting.com/actfl-proficiency-scale
A brief overview of communicative competence: https://www.thoughtco.com/what-is-communicative-competence-1689768
A video about the communicative competence model: https://study.com/academy/lesson/communicative-competence-definition-model.html