/usr/share/lightning/extensions/langpack-ga-ie@lightning.debian.org/chrome.manifest is in lightning-l10n-ga-ie 1:52.9.1-1~deb9u1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 | locale calendar ga-IE jar:chrome/ga-IE.jar!/locale/ga-IE/calendar/
locale lightning ga-IE jar:chrome/ga-IE.jar!/locale/ga-IE/lightning/
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