FR: .po file summary in file blob view

[MichaelChirico]

.po files are a key piece of the gettext system of library translation. They have a relatively simple structure.

I think it would be super helpful for i18n teams to provide a simple "progress summary" at the top of the blob file view of such a file when loaded, e.g. this file

https://github.com/r-devel/r-svn/blob/master/src/library/base/po/R-ja.

could add a simple summary at the top

I'm inspired here by the repo-level language breakdown:

Thanks for your support for i18n!