Difference in difficulty per crown for different languages
I am currently working through 10 different trees here on duolingo and noticed that based on the language you are learning the amount of lessons/quizzes you need to go up a crown is different. The tree I am finding to be the most difficult is Japanese. This is not because of the difficulty of the language though as it is by far my best language (I am married to a Japanese individual and have been living and working in Japan for over 6 years). For example to go from level 2 to 3 on Spanish you need an average of 8 quizzes but for the same crown requirement on Japanese you need 14 quizzes. Some of the other languages I am doing are in between with an average of 10 or 12. I switched from leveling up a particular skill on Japanese to just trying to clear the tree which has given me a lot of crowns. I have a very similar number of crowns in Spanish but have only completed half of the tree. I want to know if there is a particular reason for this.