In SERVER-26072 we added collation support for additional locales, such that we now support all collators which are supported by ICU 57.1. The 3.3.x release series notes need to be updated accordingly.

SERVER-26072 lists the locale ids for the added locales. See the collators tab of the ICU Data Library Customizer for the name of the language associated with each added locale id. This information is also available via the CLDR data here.