Oh, hey, yep. Tripping over my own ignorance there.
I didn't realize that latest-mozilla-central-l10n/ subdirectory existed; I've always gone straight for latest-trunk/, which it turns out is a symlink to latest-mozilla-central/, which only contains the en-US builds. Thanks for pointing that out. I'll file a bug to get https://nightly.mozilla.org/ updated to point to the localized builds.
I didn't realize that latest-mozilla-central-l10n/ subdirectory existed; I've always gone straight for latest-trunk/, which it turns out is a symlink to latest-mozilla-central/, which only contains the en-US builds. Thanks for pointing that out. I'll file a bug to get https://nightly.mozilla.org/ updated to point to the localized builds.