[l10n] Improve Japanese (ja-JP) locale

[yuito-it]

ChangeLog

• Add Japanese locale translations

• [x] I have followed (at least) the PR section of the contributing guide.

[mui-bot]

Localization writing tips :writing_hand:

Seems you are updating localization :earth_africa: files.

Thank you for contributing to the localization! :tada: To make your PR perfect, here is a list of elements to check: :heavy_check_mark:

• [ ] Verify if the PR title respects the release format. Here are two examples (depending if you update or add a locale file)

  [l10n] Improve Swedish (sv-SE) locale [l10n] Add Danish (da-DK) locale

• [ ] Update the documentation of supported locales by running pnpm l10n
• [ ] Clean files with pnpm prettier.

Deploy preview: https://deploy-preview-20251--material-ui-x.netlify.app/

Bundle size report

Bundle	Parsed size	Gzip size
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@mui/x-data-grid-pro	0B(0.00%)	0B(0.00%)
@mui/x-data-grid-premium	0B(0.00%)	0B(0.00%)
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@mui/x-charts-pro	0B(0.00%)	0B(0.00%)
@mui/x-charts-premium	0B(0.00%)	0B(0.00%)
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@mui/x-tree-view	0B(0.00%)	0B(0.00%)
@mui/x-tree-view-pro	0B(0.00%)	0B(0.00%)

Details of bundle changes

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