data_dir seems to wrongly be local.

[gl-yziquel]

This is a bug coming from the just tool:

casey/just#2212

It seems that data_dir() returns some local folder such as /home/mini-me/.local/share and not some system wide folder such as /usr/local/share.

Maybe there is something that I don't quite get, but this seems to more or less be intended behaviour, when looking at the codebase of dirs-rs.

[soc]

Correct.

There are some platforms (like Windows) that distinguish(ed) between user data that's stored on the machine and user data that is associated with a user account and synced to the machine when the user logs in.

data_dir vs. data_local_dir allows you to select the appropriate one, even if it may not make a difference on the operating system you are currently running on.
(Similar with config_dir vs. preferences_dir.)