CiteprocLocaleNotFound: C.UTF-8 when running pandoc --from=biblatex --to=csljson on GitHub Actions

[dhimmel]

Using Pandoc 2.11.1.1 on a GitHub Actions ubuntu-18.04 image, I get an error CiteprocLocaleNotFound: C.UTF-8 when running the following command (CI log):

pandoc --from=biblatex --to=csljson /home/runner/work/manubot/manubot/manubot/pandoc/tests/bibliographies/bibliography.bib

The same command on a GitHub Actions build on macos-10.15 completes successfully.

This issue is reminiscent of jgm/pandoc-citeproc#420

[dhimmel]

noting a workaround in manubot/manubot@b980d15:

env:
  LANG: en_US.UTF-8  # https://github.com/jgm/citeproc/issues/26