Bug 1901118 - Port bug 1900421: Pull Toolkit/Devtools strings from Github. r=dandarnell

Differential Revision: https://phabricator.services.mozilla.com/D212863

--HG--
extra : moz-landing-system : lando

testing/mozharness/configs/single_locale/thunderbird_split_l10n.py

@@ -8,6 +8,8 @@ config = {
     "mozconfig_variant": "l10n-mozconfig",
     # Used to get toolkit & devtools strings
     "hg_l10n_base": "https://hg.mozilla.org/l10n-central",
+    # If set, takes precedence over `hg_l10n_base`
+    "git_repository": "https://github.com/mozilla-l10n/firefox-l10n",
     # URL of comm-l10n monorepo
     "hg_comm_l10n_repo": "https://hg.mozilla.org/projects/comm-l10n",
     "locales_dir": "comm/mail/locales",