https://www.dynadot.com/help/question/what-is-IDN
IDNs are domains with non-ASCII characters such as Chinese or Japanese. We support IDNs in a variety of languages and we also support IDN extensions!
internationalized domain nameidnnames
https://letsencrypt.org/2016/10/21/introducing-idn-support.html
Let’s Encrypt is pleased to introduce support for issuing certificates that contain Internationalized Domain Names (IDNs). This means that our users around the...
internationalized domain nameintroducingidnsupportlet