Duolingo DE from EN versions:

Trees:
v0: 2011-11-30  ? (Beta)
v1: 2012-06-19, ?
v2: ?
v3: 2015-12-15, 121 Skills (121 Different lessons)
v4-v9: ?
v10: 2020-09-10, 133 Skills (133 Different lessons)
v?: 2021-03-29, 149 Skills (149 Different lessons)
v?: 2021-04-04, 160 Skills (160 Different lessons)
v?: 2021-09-11, 178 Skills (178 Different lessons)
v?: 2022-04-01, 137 Skills (137 Different lessons)

Paths (all CEFR B2):
1.0: 2022-09-10, 113 Skills and 158 stories = 271 Different Lessons (114 units, CEFR B1)
2.0: 2022-12-09, 155  Skills and 187 stories = 342 Different Lessons (131 units, CEFR B1)
3.0: 2023-09-10, 150  Skills and 187 stories = 337 Different Lessons (102 units, CEFR B1)
4.0: 2024-02-02, 137 Skills and 143 stories = 280 Different Lessons (89 units, CEFR B1)
2.1: 2024-02-15, 155 Skills and 187 stories = 342 Different Lessons (178 units, CEFR B1)

tree_de_en_v2_experiment
tree_de_en_v3_experiment
tree_de_en_v4_experiment
tree_de_en_v5_experiment
tree_de_en_v7_experiment
tree_de_en_v8_experiment
tree_de_en_v9_experiment
tree_de_en_v10_experiment
tree_de_en_v11_experiment
tree_de_en_v12_experiment
tree_de_en_v13_experiment
tree_de_en_v14_experiment
tree_de_en_v15_experiment
tree_de_en_v17_experiment
tree_de_en_v18_experiment
tree_de_en_b1_2_existing
tree_de_en_b1__2_new

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.