www.coe.int/lang-CEFR: the result of over twenty years of reserach, the Common European Framework of Reference for Languages, assesses language levels.

https://www.alte.org/ Association of Language Testers in Europe.

https://www.actfl.org/ standard measure of proficiency in academia and international business settings. 

https://www.govtilr.org/ language proficiency scale mainly used in the United States.