[i18n] Setup en-fallback for sections other than docs

[chalin]

Set up English fallback pages for (top-level) sections other than docs as enough non-en locales have sufficiently translated content:

• Trainging
• Ecosystem
• ...

[vitorvasc]

We already have some localizations for the Training page -- was this issue meant to cover configs for supporting localized content under content/[lang]/training?

Or is the idea more general, to track localization across all the languages we currently support?

[chalin]

I've updated the opening comment to clarify the main intent, which is to set up a fallback page so that the Training top-nav entry shows up in all locales.

[svrnm]

this is still pending right?