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