In your Transifex settings you can set e-mail notifications when a resource in one of your projects is updated. That usually means new strings to translate.
As for the lack of community in Transifex, I’d encourage everyone to make topics for any translation questions here. After all you’ll also find people here who might know answers but are not active on Transifex.
Most style guidelines don’t change for years. A solution might be to only show a translated guideline when it is up to date.