UI messages can now be blank, this is now considered to be different to
missing. Unless there are strenuous objections, it will stay that way, I
think it makes more sense than those ugly workarounds.
There were a few transient bugs over the last 24 hours related to this,
some messages erroneously showed up as blank when they were in fact
missing. This should be fixed now (thanks to Brion for helping with this).
I also improved the cache a bit.
-- Tim Starling