I just installed this language pack:
http://imaginaerum.github.io/magento2-language-fr-fr/en.html#section-installation
The way I installed it was like this: 1. create folder via ftp in app/i18n/imaginaerum/fr_fr/ unzip file here 2. create store view and change language to french (france).I used language code "fr"
it works.
I'm curious how Magento knew to use that folder as a language pack. It seems to me I did nothing to really connect the language choice with that pack. And while it is doing exactly what I want I don't know how/why so I am kind of curious as I am just starting to learn how magento works.