Issue #12732: trying to fix gettext usage

Not to be merged in this state. It's based on the fact that gettext release notes may actually give a solution: The default value of 'escape' in the gt:escapeRule was "yes"; now it is "no". And it turns out we had this at "no", but probably because xgettext was doing the escaping rule (so avoiding it done twice). Now we must set this back to "yes".

On my machine, setting this to "yes" though breaks the setup.isl.xml. I'm hoping it fixes on CI which uses a different gettext version.

If it works, we'll have to add some gettext version check in the meson scripts.