Collect and add external translation resources to the L10n wiki

As discussed during the Tor Localization Hangout, we intend to add external translation resources to our wiki. We already added a couple of entries: https://gitlab.torproject.org/tpo/community/l10n/-/wikis/Localization-for-translators#external-translation-resources

If you're aware of any such tools, resources, tips, etc. please feel free to comment on the ticket with a link and a brief description of the tool. Thanks!