I am not sure you want to disable everything.
Some are quite useful even in release.

Why would JavaScript in gui folder need to directly read or write into l10n, fonts or shader files?
Those functions are not about if you can get info from somewhere or update something. It is about the script interface designed for the task cannot be bypassed by direct access to the files mainly because given interface may want to do certain checks or apply anything before returning result back to the js.

Also, possibly it would be good to make some mock technology and unit template just for test so it will not come invalid when someone tries to do balancing or removes it

Nullish coalescing is denoted by double question marks (??).

Was fixed already, reopening ticket because it's broken again
#6294

What if it would be halfed instead of removed?

So are now buildings stuck with variants depending on the season? Or can there be variants inside those variants?

For future:

If they can lead to the same problem, they should be fixed here

In case of actor > group > group > group it's easier to add a bug

That can be solved by allowing only "actor > groupref > group" or "actor > group" so no group chain can be created