Input validation becomes much harder in international products. Locale-aware regex avoids rejecting valid names, addresses, and identifiers from non-English markets.

Do Not Assume Latin-Only Input

Use Unicode properties and normalization-aware comparisons. ASCII-only assumptions often create exclusionary UX.

Separate Format from Semantic Validation

Regex should verify shape, while locale/business rules verify meaning (for example region-specific postal code constraints).

Plan for Mixed-Script Edge Cases

Some fields should allow mixed scripts; others should not. Define policy per field instead of globally.

Test with Locale Fixtures

Maintain representative fixture sets across major locales to prevent regressions when patterns evolve.