Template search algorithm always prefers localized templates over default english ones

When I have localized german templates at config.TEMPLATE_DIR/site/de and set server-wide default language to 'de', this causes mailman to always take the german templates, even if the configured language for a list is english.

In my case, this leads to errors since the default encoding for english lists is us-ascii but our german templates are utf-8 encoded.

I think, it would be better to use the default english templates if the prefered langauge (either list-specific or user-specific) is english, even if the server-wide default language is different.

This needs to be fixed in mailman.utities.i18n.search().