https://discourse.gnome.org/t/millions-plural-form-in-french-spanish-portuguese-italian/12867

I can't remember what these things do and I wrote all this.

Render them as a single legible message, not a huge traceback, and
summarize at the end of the run (along with a non-0 exit status).

This is useful when a few languages have syntax errors, but you want to
process the rest.

Previously, on encountering a file that polib cannot parse, there was no
indication (without --debug) of which file is causing offence:

    Traceback (most recent call last):
      File "../../wjt/translate-o-tron-3000/t3k", line 296, in <module>
        main()
      File "../../wjt/translate-o-tron-3000/t3k", line 292, in main
        args.func(args)
      File "../../wjt/translate-o-tron-3000/t3k", line 170, in rebase
        git_show_rev_file(args.git_dir, args.base_rev, rel_path)
      File "/usr/lib/python3/dist-packages/polib.py", line 139, in pofile
        return _pofile_or_mofile(pofile, 'pofile', **kwargs)
      File "/usr/lib/python3/dist-packages/polib.py", line 87, in _pofile_or_mofile
        instance = parser.parse()
      File "/usr/lib/python3/dist-packages/polib.py", line 1428, in parse
        (fpath, self.current_line))
    OSError: Syntax error in po file (line 2340)

Since we are passing the contents of the file to pofile(), not its path,
the 'fpath' visible in the backtrace is the empty string – polib doesn't
know what it's called. Even though the (private) POFile constructor
accepts a fpath argument to deal with this case, the pofile() wrapper
function doesn't pass it through; and it would be cheating to tell it a
path that is not actually an on-disk file. Rather than materializing the
file, we can just include the revision and path ourselves:

    Traceback (most recent call last):
      File "../../wjt/translate-o-tron-3000/t3k", line 158, in _parse_pofile_at_rev
        return polib.pofile(contents)
      File "/usr/lib/python3/dist-packages/polib.py", line 139, in pofile
        return _pofile_or_mofile(pofile, 'pofile', **kwargs)
      File "/usr/lib/python3/dist-packages/polib.py", line 87, in _pofile_or_mofile
        instance = parser.parse()
      File "/usr/lib/python3/dist-packages/polib.py", line 1428, in parse
        (fpath, self.current_line))
    OSError: Syntax error in po file (line 2340)

    The above exception was the direct cause of the following exception:

    Traceback (most recent call last):
      File "../../wjt/translate-o-tron-3000/t3k", line 309, in <module>
        main()
      File "../../wjt/translate-o-tron-3000/t3k", line 305, in main
        args.func(args)
      File "../../wjt/translate-o-tron-3000/t3k", line 185, in rebase
        base = _parse_pofile_at_rev(args.git_dir, args.base_rev, rel_path)
      File "../../wjt/translate-o-tron-3000/t3k", line 160, in _parse_pofile_at_rev
        raise IOError(f"Failed to parse {rev_filename}") from exc
    OSError: Failed to parse 3.26.7:po/ca.po

This makes instructions easier to write.

t3k for short.