Rerouted (regenerated, verified). Same repository and tag, but GitHub now builds the zip with different bytes, so it no longer matches the SHA-1 package.elm-lang.org recorded. The Lamdera package server serves a copy recovered from https://github.com/miniBill/date-format-languages.
What we checked: Tag 1.2.0 is still on github.com/miniBill/date-format-languages; its commit 19b2c0b12430 is from 2019-09-19 13:48 UTC, before the version was published (2019-09-19 13:49 UTC); elm.json is byte-identical to package.elm-lang.org's; the exposed modules match docs.json; the zip's SHA-1 is not the published one (GitHub's zip no longer comes out byte for byte the same), so the contents were checked instead.
The Lamdera compiler uses this copy and prints a one-line notice saying so. elm itself fails to download this version.
Details · package.elm-lang.org's zip: https://github.com/miniBill/date-format-languages/zipball/1.2.0/
Companion package for ryannhg/date-format. This package contains the languages.
elm install miniBill/date-format-languagesPublished on 19 Sep 2019 under the BSD-3-Clause license.
Elm version 0.19.0 <= v < 0.20.0
Rerouted (regenerated, verified): the zip served is the recovered copy, SHA-1 02facbb2163debb1e951f9a793a14086ee5fb597.
Files: elm.json · docs.json · endpoint.json · README.md · releases.json