localization_extensions.dart

import 'package:flutter/material.dart';

extension LocaleFallbackExtensions on Locale {
  /// Look up the most specific version of a localized string, falling back through the BCP 47 language-script-region hierarchy.
  String? getString(String? key, String? Function(String k) lookup) {
    final prefix = key != null ? '${key}_' : "";
    String? text;

    if (null != (text = lookup('$prefix${toString()}'))) {
      // full locale code (en_US, es_MX, fr_CA, zh_Hans_CN, zh_Hant_TW)
      return text;
    }

    // additional fallback if we have something besides languageCode
    if (scriptCode != null || countryCode != null) {
      // if we have both a script (Hans) and country (CN), try both fallbacks
      if (scriptCode != null && countryCode != null) {
        if (null != (text = lookup('$prefix${languageCode}_$countryCode'))) {
          // zh_CN (without scriptCode)
          return text;
        }

        if (null != (text = lookup('$prefix${languageCode}_$scriptCode'))) {
          // zh_Hans (without countryCode)
          return text;
        }
      }

      if (null != (text = lookup('${key}_$languageCode'))) {
        // zh (languageCode only)
        return text;
      }
    }

    if (key != null) {
      // no localized string was found, so get the default
      return lookup(key);
    }

    return null;
  }

  /// Find the best localized version in a set of strings.
  String? localize(Map<String, String>? localizedStrings, String key) =>
      localizeDynamic(localizedStrings, key);

  /// Find the best localized version in a dynamic map of strings.
  String? localizeDynamic(dynamic map, String key) =>
      map == null ? null : getString(key, (k) => map[k]);
}

extension BuildContextLocalizationExtensions on BuildContext {
  /// Find the best localized string in a set of strings.
  String? getLocalizedString(
    Map<String, String>? localizedStrings,
    String key,
  ) {
    return Localizations.maybeLocaleOf(this)?.localize(localizedStrings, key) ??
        localizedStrings?[key]; // no locale for the context, so get the default
  }

  /// Find the best localized string in a dynamic map of strings.
  String? getLocalizedStringDynamic(
    dynamic map,
    String key,
  ) {
    return Localizations.maybeLocaleOf(this)?.localizeDynamic(map, key) ??
        map?[key]; // no locale for the context, so get the default
  }
}