The Common European Framework of Reference for Languages: Learning, Teaching, Assessment is a guideline to measure achievements in European languages. For information about the background to the CEF see this Wikipedia article.

Levels

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A Basic User
A1 Breakthrough (often known as Elementary)
A2 Waystage (often known as Pre-Intermediate)
B Independent User
B1 Threshold (often known as Intermediate)
B2 Vantage (often known as Upper Intermediate)
C Proficient User
C1 Effective Operational Proficiency (often known as Advanced)
C2 Mastery (often known as Proficiency)