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Three locales — de, fr, en — and two distinct mechanisms.

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UI chrome: next-intl message files

Message files live in src/messages/{de,fr,en}.json.
Namespace keys as module.section.key.

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All three files, together

A key added to de.json without en.json and fr.json is a runtime error for non-German users. The parity gate compares the full nested key tree of all three files and fails CI on a mismatch:
Never hardcode a German, French or English string in component JSX or in a service return value that reaches the UI. That includes error messages, button labels, table headers and placeholder text.

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Authored content: per-locale fields

Anything a person reads that your customer wrote — e-mail templates, portal messages and notifications, job ads, pipeline stage instructions, offer letters, generated documents, survey and feedback questions. These are stored in per-locale fields on the record: field, fieldEn, fieldFr. Every such surface must ship with the shared TranslateButton (@/components/translate-button), which drafts the other locales from the one the user wrote for review before publication.
A single-locale communication surface is not acceptable. If a feature sends an applicant or an employee something they read, it must be authorable in all three languages.

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Recipient locale wins

Outbound communication renders in the recipient’s locale, not the sender’s. The notification dispatcher resolves the recipient’s locale before rendering. Where a dispatch is recorded — probation questionnaires, payslip mails — the wording actually used is snapshotted on the dispatch row, so the record shows what the person received rather than what the template says today.

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Testing

Component tests use a stable intl mock, checked by its own guard (npm run check:stable-intl-mock) so a test cannot accidentally depend on a non-deterministic translation shim. Assert on the translation key or on a stable test id, not on translated prose — a test that breaks when a comma moves in de.json is testing the wrong thing.

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Adding a key

1

Pick the namespace

module.section.key, matching where the string is used.
2

Add it to all three files

Same path in de.json, en.json, fr.json.
3

Use it

useTranslations or getTranslations.
4

Verify

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Formats

Locale affects dates, number separators and currency formatting. CHF is the currency throughout; the formatting helpers in src/lib/formatting/ handle the locale mapping. Number separators matter on payroll exports, where a mis-parsed separator is a mis-stated amount.