Duolingo UK from EN versions:

Trees:
v0: 2014-08-19, ?  (Beta)
v0: 2015-05-21, ?  (Beta)
v1: 2017-02-12, 51 Skills (51 Different Lessons)

Paths:
1.0: 2022-09-10, 51 Skills (51 Different Lessons) (33 units)
1.1: 2023-09-10, 51 Skills (51 Different Lessons) (33 units)
1.2: 2024-05-01, 51 Skills (51 Different Lessons) (58 units)

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, 2024-05-02.