Create script to check translations have been provided

[eleanorreem]

Overview

As a dev, I get helpful warnings if I forgot to add a translation file or to paste translations in the relevant files.

Currently, when an english translation file is added to the /messages folder for a new page, the spanish / hindi equivalent could easily be missed. It would be great to run a script to check that all the files match up.

Action Items

• [ ] Add a script which checks that our translation files are correct. This script needs to check that
• [ ] for each enabled language that the messages .json files exist for every folder. i.e. shared/en.json, shared/hi.json etc.. all exist.
• [ ] for each file, ensure there is a matching key value pair in every file.
• [ ] if either of these is not true, print a warning mentioning, language and the key.
• [ ] Add the script to the package json. It should be called something like "check:translations".