/usr/lib/x86_64-linux-gnu/vala-panel/applets/pager.plugin is in vala-panel-plugins-wnck 0.3.65-0ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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Module=pager
Name[ru]=Переключатель рабочих столов
Name=Pager
Description[ru]=Показывает рабочие столы
Description=Shows desktops.
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