How well do you think scaling would work in, say, evaluating capacity to write or read academic or professional material? What, if any adaptations, would be necessary?
Benchmarks for evaluating language skill level by scaling:
Level 5 (educated native speaker): no trouble using the language.
Level 4 (advanced): reads, writes, speaks, and understands with few
errors. At ease in the milieu.
Level 3 (advanced intermediate): Adequate skills in most subjects, but
better in some areas than others.
Level 2 (lower intermediate) can communicate (with difficulty) in some
Level 1 (beginner) little or no familiarity with the target language.
report on validity of self-rating