Fixed #23271 -- Don't corrupt PO files on Windows when updating them.

Make sure PO catalog text fetched from gettext programs via standard
output isn't corrupted by mismatch between assumed (UTF-8) and real
(CP1252) encodings. This can cause mojibake to be written when creating
or updating PO files.

Also fixes #23311.

Thanks to contributor with Trac nick 'danielmenzel' for the report,
excellent research and fix.