chore: update i18n contributing guide

[userquin]

This PR includes the following changes to CONTRIBUTING.md file:

• add link to unicode.org plural rules spec
• use underscore instead dash for translation keys
• don't concatenate strings in vue templates: link to vue-i18n component and some examples
• fix some typos (coderabbitai)

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ All tests successful. No failed tests found.

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[coderabbitai]

📝 Walkthrough

Walkthrough

The CONTRIBUTING.md was updated to expand localisation guidance. The "Adding a new locale" step now references both a Pluralization rule callback and a separate Plural Rules resource. Guidance was added under "Update translation" and "Adding translations" explaining placeholder usage, advising against string concatenation in templates, recommending the i18n-t utility for complex content, and providing bad/good examples and a complex-content scenario. Translation key conventions were changed to prohibit dashes and require underscores (for example privacy_policy instead of privacy-policy).

Suggested reviewers

• danielroe
• whitep4nth3r

🚥 Pre-merge checks | ✅ 1

✅ Passed checks (1 passed)

Check name	Status	Explanation
Description check	✅ Passed	The pull request description accurately relates to the changeset, detailing all main modifications to CONTRIBUTING.md including pluralization rules, translation key conventions, vue-i18n guidance, and typo fixes.

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✨ Finishing touches

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[coderabbitai]

Actionable comments posted: 1

Caution

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⚠️ Outside diff range comments (1)

CONTRIBUTING.md (1)

348-348: ⚠️ Potential issue | 🟡 Minor

Fix typo: “then English” → “the English”.
Minor grammar issue in the sentence about outdated translations.

[coderabbitai]

Actionable comments posted: 1

🧹 Nitpick comments (1)

CONTRIBUTING.md (1)

427-442: Consider clarifying the complex content example.

The i18n-t example references translation keys (terms_link and privacy_policy) that aren't shown in the JSON snippet on line 430. Contributors might find it clearer if the example included the complete JSON structure.

📖 Suggested enhancement for clarity

+   **Example JSON:**
+
    ```json
-   { "agreement": "I accept the {terms} and {privacy}." }
+   {
+     "agreement": "I accept the {terms} and {privacy}.",
+     "terms_link": "Terms of Service",
+     "privacy_policy": "Privacy Policy"
+   }
    ```

+   **Example Vue template:**
+
    ```vue
    <i18n-t keypath="agreement" tag="p">
      <template `#terms`>
        <NuxtLink to="/terms">{{ $t('terms_link') }}</NuxtLink>
      </template>
      <template `#privacy`>
        <strong>{{ $t('privacy_policy') }}</strong>
      </template>
    </i18n-t>
    ```

[coderabbitai]

Actionable comments posted: 1

[coderabbitai]

Actionable comments posted: 1