1. We must always output all (diverging) options, including
default options; if not, default options might get overwritten.
2. Do not output options in \setotherlanguage, since we might have
multiple "other languages" varieties from the same language (such
as naustrian, nswissgerman). And the options are output for the
language switches anyway.
Hence, LaTeXFeatures::getPolyglossiaLanguages() does not have to record
varieties. This was not done correctly anyway, since the map allowed
for one entry per language only.
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