I18n: Pluralize remaining unpluralizable strings

[tristanlabelle]

These were the last few placeholder numbers that didn't support pluralization. Two reasons to pluralize them:

• Pluralization isn't just for 1 vs many, in some languages a number ending with 2 like 102 will have a different plural form than a number ending in 6 like 106, similar to English's 102nd vs 106th.
• All strings now provide the right example for adding future strings.

I changed the keys because the placeholder's name changed, so we can't reuse existing translations.

I also changed the "65k+" placeholder in favor of formatting the 65000 number because "65k+" is not localized. I assume we're not too concerned about that code path, which implies a backend bug.

Testing

Backend checklist

• Added tests for any new code or added a regression test if fixing a bug
• Run the backend locally and it works
• Added migrations if there are any database changes, rebased onto develop if necessary for linear migration history

Web frontend checklist

• There are no console warnings when running the app
• Added tests where relevant
• Clicked around my changes running locally and it works
• Checked Desktop, Mobile and Tablet screen sizes

For maintainers

• Maintainers can push commits to my branch
• Maintainers can merge this PR for me

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Project	Deployment	Actions	Updated (UTC)
couchers	Ready	Preview	Mar 16, 2026 1:46am

[aapeliv]

lgtm, thanks for fixing!

[github-actions]

📝 Release Notes

This PR does not need to be included in release notes.

Reason: This PR mainly updates localization/pluralization handling for existing UI and error strings, plus documentation. While it improves translation quality in some languages, it is a minor internationalization/internal text change rather than a significant end-user feature, major UX improvement, important bug fix, or major technical infrastructure change.

🤖 Bot Debug Information

Model: couchers.openai.gpt-5.4
Decision: exclude
Reasoning: This PR mainly updates localization/pluralization handling for existing UI and error strings, plus documentation. While it improves translation quality in some languages, it is a minor internationalization/internal text change rather than a significant end-user feature, major UX improvement, important bug fix, or major technical infrastructure change.