As the excerpt states, the languages tag is intended for language support by the Android system and keyboards.
- languages supported by the Android system (and how to enable/set them). Might be connected with the settings tag, if applyable.
- languages supported by keyboards and other input methods. Might be connected with the keyboard or input-methods tag, if applyable.
It does not include:
- apps supporting a given language. See: localization
- if your question is about adding a language (to the system/keyboard/input methods), you might want to add the installation tag along.