bpo-39464: Allow translating argument error messages

[DjMorgul]

Argument error messages display the untranslatable text 'argument ', which should be translatable to other languages, just like it's possible to do with the rest of the constructed error message.

https://bugs.python.org/issue39464

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@DjMorgul

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[brandtbucher]

Thanks for your time @DjMorgul, and welcome to CPython! 😎

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[brandtbucher]

I don't think this is necessary... we don't internationalize any other exception messages in this file.

If this exception is raised during parsing, it is printed by calling ArgumentParser.error, which performs this step already (see the last line of the file).

It would be great if you could open a BPO issue for discussion.

[DjMorgul]

This message isn't used (only?) in exceptions... it's a message that is given to the console, to notify the user when she didn't provide correct parameters. For example:

$ python3 ./drt.py -l
Uso: ./drt.py [-h] [-l LONG_MIN] [-L LONG_MAX] [-v] [-V]
              entrada.json [salida.tok]
./drt.py: error: argument -l/--min-length: se esperaba un parámetro

These are console messages localized into Spanish. The "error:" part is translatable, but it's the same word in Spanish than in English. The "argument" part is what isn't translatable, and it's taken from this "exception".

I confirmed that my proposed patch, translating that particular string, allows giving a fully localized console output to the user in Spanish, such as:

./drt.py: error: parámetro -l/--min-length: se esperaba un parámetro

[taleinat]

@DjMorgul, the place to discuss this is on our issue tracker. Please create an issue on bugs.python.org, as suggested above by @brandtbucher.

[csabella]

@DjMorgul, did you have a chance to open an issue on the bug tracker as requested by @taleinat? If so, please update the PR title with the format bpo-xxxxx: for the tracker number. Thanks!

[DjMorgul]

I just created the issue on bugs.python.org, and I updated the title of this pull request accordingly.