[Plastic-time]

With zh_CN active, intword(10**15) currently returns 1.0 万亿; zh_HK returns 1.0 萬億. Those labels mean 10**12, so the displayed quantity is a thousand times too small. Cambridge's definition of quadrillion is 1,000,000,000,000,000 (1000万亿 / 1000萬億).

Changes proposed in this pull request:

• Correct both plural entries to 千万亿 and 千萬億 in the respective catalogs.
• Extend the existing localization tests with positive, negative, plural and rounding-to-quadrillion cases, plus checks that the neighboring trillion and quintillion labels stay unchanged.

Before the catalog change, eight new cases fail and four neighboring-scale cases pass. After recompiling the catalogs, all twelve pass.

Validation on Windows, CPython 3.12.14:

• Full tests and source doctests, with benchmark timing disabled: 903 passed, 2 skipped. The two translation-update tests require GNU gettext command-line tools that are unavailable locally; all 36 catalogs were compiled with polib, and the Chinese regression tests ran.
• All applicable configured prek hooks passed over the full repository.
• Mypy passed for all 14 source files; git diff --check passed.

This is based on current main and is independent of the missing translations in #472. The placeholder migration in #403 touches these entries but retains the incorrect labels; if that merges first, this correction will need to be carried over to its new message IDs.

Prepared and tested with OpenAI Codex assistance. Other platforms and Python versions were not run locally.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.70%. Comparing base (a2006ea) to head (30ca107).

Additional details and impacted files

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##             main     #473   +/-   ##
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  Coverage   99.70%   99.70%           
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  Files          12       12           
  Lines        1020     1020           
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  Hits         1017     1017           
  Misses          3        3           

Flag	Coverage Δ
macos-latest	97.25% <ø> (ø)
ubuntu-latest	97.25% <ø> (ø)
windows-latest	92.35% <ø> (ø)

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