Remove `KIWIX_DATA_DIR`

[kelson42]

To me this ENV variable KIWIX_DATA_DIR:

• Is not clear which feature it serves (seems useless to me)
• I'm again to instrument Kiwix Desktop with "hidden" variable environnements.
• Is not documented (the best doc I have is this comment from @veloman-yunkan )
• As a bad naming because only part of the data are stored in it

For all this reasons, I ask if we should just not remove it?

This is a follow-up of https://github.com/kiwix/kiwix-desktop/pull/1081 and https://github.com/kiwix/kiwix-desktop/issues/694

[mgautierfr]

Is not clear which feature it serves (seems useless to me)

It is a way to configure libkiwix and overide the resolution order of getDataDirectory

I'm again to instrument Kiwix Desktop with "hidden" variable environnements.

It is a libkiwix feature, which is used by kiwix-desktop

Is not documented (the best doc I have is https://github.com/kiwix/kiwix-desktop/issues/694#issuecomment-2049562023 from @veloman-yunkan )

Documented here : https://libkiwix.readthedocs.io/en/latest/api/function_tools_8h_1ab559be1bc8eca66c26901660949870c0.html

As a bad naming because only part of the data are stored in it

I would say that it would be to kiwix-desktop to always use the directory returned by kiwix::getDataDirectory unless specific config changed that (and fix kiwix-desktop if it is not the case (whatever we decide about KIWIX_DATA_DIR))

[kelson42]

@mgautierfr Thank you for the clarification, I have moved the issue. The documentation link is also very helpful to understand. I have created an issue to request a proper documentation of all local paths to save/load things in the Wiki https://github.com/kiwix/kiwix-desktop/issues/1114