Duolingo KL from EN versions:

Trees:
v0: 2014 Started development
v0: 2015-04-09  ? (Beta)
v1: 2015-01-16, 30 Skills (30 Different lessons) (Beta)
v2: 2018-03-15, 36? Skills (beta)
v3: 2019-09-07, 62 Skills (62 Different lessons) (Beta)
v4: 2021-09-07, 65 Skills (65 Different lessons) (Beta)

Paths:
1.0: 2022-09-10, 62 Skills (62 Different lessons) (Beta) (40 Units)
2.0: 2022-09-10, 65 Skills (65 Different lessons) (Beta) (41 Units)
2.1: 2023-09-10, 65 Skills (65 Different lessons) (Beta) (43 Units)
1.2: 2024-05-01, 65 Skills (65 Different Lessons) (74 units)
1.3: 2024-05-10, 65 Skills (65 Different Lessons) (65 units)
1.4: 2025-07-08, 65 Skills (65 Different Lessons) (65 units) CEFR A1

tree_tlh_en_v1_experiment
tree_tlh_en_v2_experiment
tree_tlh_en_v3_experiment
tree_tlh_en_v4_experiment

https://www.kli.org/duolingo/
https://liuch.github.io/duolingo_courses_overview/
https://duolingo.fandom.com/wiki/Course_list
https://duolingodata.com/
https://duolingodata.com/oldtable.html
https://ardslot.com/duolingocrowns.html

Edited by Mat!/Ozone, 2025-07-09.