Fix setting fonts on OS X

Clicking the checkbox would cause saving preferences _before_ the face
was sent, in which case SaveValues() saved it as unchecked (because the
font was invalid). Then when the user clicked to change the face, a
modal window shows up and when dismissed, the generated activate event
would cause _loading_ of preferences, where the checkbox was saved as
off. This was "only" a problem when setting custom font initially, i.e.
in the common case.

Fix by always having some valid font in there.
Better phrasing of missing spellchecker prompt

Don't tell they user that they "have to" do something. Also show the
language in a more natural form, instead of the full locale name of
Language (Country, Variant).