https://bugzilla.wikimedia.org/show_bug.cgi?id=63327
--- Comment #1 from Merlijn van Deen valhallasw@arctus.nl --- One of the reasons we are using the current file format is the structure: in pywikibot, the typical use case is 'getting a few strings from a lot of languages', while the general use case (e.g. for mediawiki) is 'getting a lot of strings from a single language'.
On tools-login, parsing all mediawiki's json files takes 3-5 seconds. For many bot users, this might be a lot longer (slower computer, slower hard drive), which (I think) is not reasonable.
Switching to a json-based format with the same file structure would be OK with me.