Other countries that have plain English standards

In the UK, the Plain Language Commission has a Clear English Standard logo. And the Plain English Campaign has a Crystal Mark. Both have been around for over 20 years.
Plain Language Commission's website
Plain English Campaign's website

Canada has its Clear Language and Design (CLAD) mark.
CLAD's website

Internationally, lawyers have a plain English organisation called Clarity. Clarity offers accreditation on plainly written and well-designed documents.
Clarity’s website