Duolingo offers free English courses and a free practice English test that users can take online anytime, anywhere to build skills, prepare, and become familiar with the test format. However, the free courses and practice test do not provide an official certificate.
The paid Duolingo English Test provides an official English proficiency certificate for a fee. This certificate can be added to an Upwork profile using the Share Certificate option. For freelancers, it can help verify English level, build client trust, improve profile credibility, and show strong communication skills.
https://www.coursera.org/articles/duolingo-english-test