1.dart生成arb文件
flutter pub pub run intl_translation:extract_to_arb --out
put-dir=lib/i18n/intl/ lib/i18n/intl/ninghao_demo_localizations.dart
2.arb文件轉換成dart文件
flutter pub pub run intl_translation:generate_from_arb --
generated-file-prefix=ninghao_demo_ --output-dir=lib/i18n/intl/ --no-use-deferred-loading lib/i18n/intl
/ninghao_demo_localizations.dart lib/i18n/intl/intl_*.arb