Three things are held down here. The route hands the reader's language to
the strip builder, for a cookie and for a stored preference. The pattern
sentence comes back in German for a German reader, asserted word for
word, through the real chain rather than the engine on its own — the
engine could always write German, it was simply never asked, so an
engine-only test would have stayed green the whole time it was broken.
And a cached strip stays with the language it was written in.
The guard reads the declarations rather than grepping them, so renaming
the argument or moving the fallback into a variable does not slip past
it. Its counterpart runs the same detector against those disguises and
insists each one is caught, because a check that cannot fail reads like
proof and is not.