Events: Main site has translations, but site is not localized

[ryelle]

The theme for events.w.org has translations, and those are being imported into GlotPress. Translators are translating these, but since there is no Rosetta or locale switcher for this site, the translations never show up.

Strangely, that's not actually true— if a user has set their own language, for example German, the local navigation is translated. I'm not sure why that's translated when nothing else is, since most of these strings are translated.

With the current setup, we can't use the Rosetta-style subdomains, but perhaps the locale switcher from Learn can be reused here.

If so, the theme will need to be audited for translation support — at a quick glance, there are places where strings are not wrapped in translation functions, and places where the wrong textdomain is being used.

Originally raised by @timse201 in WordPress/wporg-main-2022#524