[botinc-agent]

Problem

When the caller did not set DiditConfig.languageCode, the wrapper forwarded only Locale.languageCode. The native SDKs name Simplified Chinese, Traditional Chinese and Brazilian Portuguese with their own codes, so a zh_TW or pt_BR device was sent to the generic zh/pt UI. The new test shows the old behavior (zh_TW -> zh).

Solution

• Derive the device locale code in _deviceLanguageCode(): Hant/TW/HK/MO -> zh-TW, Hans/CN/SG -> zh-CN, pt_BR -> pt-BR, otherwise the two-letter language. An explicit languageCode still wins.
• Mirror the change into the three generated variant packages.
• Add test/wrapper_contract_test.dart, covering all configuration options on both entry points, the success, cancel and failure callbacks, and transaction callback routing.

Verification

• The new locale test fails on the previous code (Expected: 'zh-TW', Actual: 'zh') and passes after the change.
• flutter analyze (root and the three variants): no issues.
• flutter test -r expanded: 39 tests pass (26 existing, 13 new).
• flutter test in example: passes.
• Not run here: iOS/Android builds (this Linux sandbox has no Xcode, Android SDK or JDK) and a staging journey (the native verification SDK targets production endpoints; only transactions accept a base URL).