You knew that by winning 100 challenges in each course you win 200XP.

Course/Code/Challenge related badges can be earned once for every language.

I did not know. thank you

The badges with: "using one weapon" are always multi-collectable (XPs)

So far I don't challenge and only publish code in Python. I guess that means the xp must be from lesson comments.

That explains why I sometimes get a bunch of XP for no apparent reason. is there any place to check your XP history or find out the reason for XP when there is no associated badge?

Check you challenge wins if you hit a win or completion at the amount where you go a badge, you should get xp.

Yes I learn that recently. Thank you for sharing!

I don't hope that we get XP for codes in each language. Is it true?

In the Sololearn website you can see each of the badges won in each course, it also indicates the level per course and your ranking in that course.

I just won my 100 challenge in PHP and they gave me 200XP, I had already won the badge with 100 won in Python

Thanks for nice question