Translating choose-mirror is not trivial
I find it common practice by new translators (like me) that country
codes in choose-mirror are not translated and just copied. (It's good
to use en.po for reference while translating.) But that's not all. I
didn't understand "US[ default..]" until Denis Barbier point me that
this is the default value for the select. All this deserves a place in
doc/translations.txt. Would someone commit some text in
doc/translations about these things?