@flodolo any advice on how to get this going? Is there pseudo locale support we can use for WE's?

Unfortunately I don't think we have anything for this (in general).

The only place we used to have pseudolocales built-in in the l10n infrastructure was Firefox OS. Gettext has its own pseudolocales, but nothing for webextension, properties, etc.

I think since we have actual localizations now, using localized builds is the best way, and let's us check other things in the process. E.g., load up in Chinese and you can easily see non-localized strings, and also do a visual check for how Chinese looks.