MAC spoofing failure notifications are not translated

Hi,

While working on #17779 (closed), I noticed MAC spoofing notifications are not translated. It is because the script runs as root, and thus does not have $LANG being set, like amnesia user.

I was thinking about the following way to solve it :

1. Read LANG from sudo -u amnesia before launching gettext.sh
2. Same, but delegating this change to some translate function in tails-shell-library
3. lazy-calling the translation, delegating it to be done only just before displaying it, with amnesia rights.

Option 3 looks cleaner to me. It could be done in tails-notify-user by making it accept arrays as arguments (to prevent issues if messages contains variables such as the mac spoofing notifications that may contains interface name etc).

Option 2 looks less relevant to me as it would involve almost as much work than 1, without IMHO real benefits.

Option 1 may be good enough, and easier if you are fine with it.