In practice we've not accepted PRs with "manual" changes of any non `en-US` locales for many years, however some (older) README/FAQ entries can perhaps be seen as actually inviting such PRs.
Now that l10n updates are running automatically via GitHub Actions, see PR 20749, we're definitely not going to accept any "manual" translation patches so it cannot hurt to de-emphasize localization in various README files.
(Also, since all relevant Fluent files have license headers it doesn't seem meaningful to mention that in the l10n README.)
Given that the mailing list has now been closed, see [bug 1340296](https://bugzilla.mozilla.org/show_bug.cgi?id=1340296), and that there's no weekly meetings any more, we probably shouldn't mention either of those in CONTRIBUTING.md.
Instead, let's just suggest the IRC channel as a means of communication here.