This allows the Spanish UI translation to work, for now, for all
Spanish speaking locales. If necessary we can make it es-ES if other
translators feel it is not a good base for their Spanish variant. OTOH
if they just need to l10n a few strings then, say for Argentina, then
they can do that in an wsjtx_es_AR.ts and untranslated strings there
will fall back to the ones in wsjtx_es.ts automatically. This happens
because of teh way the application loads multiple translation files in
an order suitable for that to happen.
