Identifying language abilities has been real popular. The “Babel templates” are quite popular on the English Wikipedia and, many of the literally hundreds of templates have been copied to other wikis.
With a limited knowledge of a language, people can be really effective execute many tasks. It helps however when they are addressed in an understandable way.
At translatewiki.net we have been using the Babel extension for a long time; it does not use any templates and all the languages used in any of the WMF projects are supported. As it has been in use for so long, it became really rich in localisations.
There have been many requests for the implementation of the Babel extension particularly by the newer and smaller projects. As people can choose to use this functionality and as it is particularly useful to people who are active on many projects, it has been implemented on all WMF wikis.
The documentation of the extension provides information about features like the inclusion of people in categories. These can be set by local admins.
Internationalization / Localization outreach consultant