Allow language spoofing in status messages

H1 user ryotac reported yet another variant of #30683 (closed), but this one is not covered by that patch because XSLT errors have their own separate bundle and displaying logic.

POC: https://people.torproject.org/~ma1/pbugs/42288/poc/

I believe in this case, rather than spoofing English in the error page, we should just match Chromium's behavior and just fail silently, displaying the untransformed document - and possibly fix upstream too, looking at this comment.

[EDIT]

In the end I decided to fix this with logic similar to #30683 (closed), instead of radically changing Firefox's behavior (potentially informative and valuable to developers debugging XML/XSLT problems) to align it with Chromium.

So in !851 (merged) we rather spoof language in XSLT error messages as well, when needed.