What are folders within sites/default/files for? There is a quite similar question in What are all the directories for in the new Drupal 8 structure? about the Drupal directory structure, but it is not explained the content of the sites/default/files directory.

Within such directory there are all these folders:


2016-01/
2016-02/
...
config_nEjJjnck1_CMDKmCKDLS9cd-CKD89cdsCD78cdsCNJD89/
css/
inline-images/
js/
languages/
php/
styles/
translations/


First two folders contains user-uploaded content. What are other folders for and how/when their content is generated? Which of these folders should be included inside a Git repository?
They're created by different parts of the system, when they're required, for pretty much anything at all that a module needs to store file-wise.

It would be pointless to try to list them all, as core/contrib/custom modules can place files/folders there arbitrarily; Drupal doesn't place any restrictions on what can/can't be stored there, it's up to each bit of code as to how and when it uses that folder to read/write.