ICU Messages and Formatting

When working with localizations in Flutter, use standardized formats rather than manual string manipulation:

ICU Syntax in ARB Files

• Use ICU plural syntax for counts (e.g., =0{No items} =1{1 item} other{{count} items}).
• Use ICU select syntax for gender or category-specific translations.
• Declare variables in the @message_key metadata block to document their types and meanings.

Locale-Aware Formatting

• Use DateFormat for timestamps and NumberFormat for values.
• Use NumberFormat.compactCurrency or NumberFormat.simpleCurrency for pricing.
• Never hardcode date patterns across locales, as conventions (e.g., MM/DD vs DD/MM) vary by region.

Fallback and Unsupported Locales

• Define a clear fallback policy in MaterialApp using supportedLocales and localeResolutionCallback.
• Ensure unsupported locales safely gracefully degrade (e.g., defaulting to English) without crashing or displaying raw translation keys.

Translatable Sentences

• Avoid string concatenation. Assemble complete sentences in the ARB file with placeholders.
• Translators must have the context of the whole phrase to properly adjust word order, which varies by language.

Testing Representative Locales

• Test layouts with long strings (e.g., German) to verify wrapping and overflow behavior.
• Test Right-to-Left (RTL) locales (e.g., Arabic) to ensure directional widgets (Row, padding) mirror correctly.
• Do not manually reverse strings or lists for RTL; rely on Flutter's Directionality.