intl: format locale-sensitive data deliberately

intl is useful because it focuses on dates, numbers, plurals, locale initialization, and testable formats. The important engineering move is to place the package behind a clear boundary, so your Flutter UI depends on a stable capability rather than a vendor-shaped API.

What the library should own

• Keep package calls inside a named adapter or feature boundary.
• Make lifecycle, errors, and loading state part of a testable contract.
• Expose only the capability the app needs; hide implementation details from the whole tree.

A focused starting point

final amount = NumberFormat.currency(
  locale: 'vi_VN',
  symbol: '₫',
).format(1250000);
final date = DateFormat.yMMMMd('en_US').format(order.createdAt);

Production checklist

1. Read the README and changelog for the exact version you pin.
2. Add one test for lifecycle, failure, and app background/foreground behavior.
3. Verify every platform your product supports, not only the developer machine.
4. Record ownership, upgrade cadence, and rollback notes in the repository.

Common pitfall

Never concatenate translated strings with numbers or dates; use ICU messages and locale-aware formatters.

Takeaway

A good open-source library does not replace architecture. It makes one difficult boundary clearer, observable, and easier to replace.