## Question Design a localization system for a product released in dozens of countries. Every user-facing string should resolve by locale, support variables and language-specific plural rules, fall back safely when a translation is absent, and allow copy updates without requiring an application release. The design must also detect missing translations and layout problems caused by longer text. ### Constraints & Assumptions - Locale may include language and region, such as `zh-TW` or `en-GB`. - Human-authored translations are primary; a default-language bundle ships with the application. - Clients cache downloaded resource bundles and may start offline. - Runtime locale switching should not require a process restart. - Dates, numbers, currencies, and plurals use locale-aware formatting rules. ### Clarifying Questions to Ask - Which clients and release versions must consume the same translation catalog? - How quickly must an edited string become visible? - Is fallback allowed for every string, or must legally sensitive text block release when missing? - Who approves translations and rollbacks? - Are experiments allowed to vary copy within one locale? ```hint Use semantic keys Map stable identifiers such as `checkout.button.confirm` to localized message templates; using English prose as the key couples copy edits to every translation. ``` ```hint Treat messages as structured templates Use a locale-aware message format for variables, selection, and plural categories instead of concatenating fragments. ``` ### What a Strong Answer Covers - Catalog schema, semantic keys, locale fallback chains, and packaged defaults. - Versioned bundle publication, client caching, integrity checks, and rollback. - Placeholder validation, plural and formatting support, and protection against unsafe interpolation. - Build-time completeness checks, runtime missing-key telemetry, and ownership workflow. - Pseudolocalization, bidirectional text, text expansion, accessibility, and visual regression testing. - Gradual rollout and behavior when remote bundle delivery fails. ### Follow-up Questions 1. How would you prevent a translator from removing a required placeholder? 2. How should a client choose among `zh-TW`, `zh`, and the default locale? 3. How would you support copy experiments without fragmenting the catalog? 4. What would you test before adding a right-to-left language?