Using Java's own Locale data for region names

Instead of having to duplicate and manually translate the region names and data with the raw xml files, Java's build-in Locale data could probably be used.

Current we are using a following trick to generate a list of localized country names for the user to select from:

// Code in Kotlin
```
Locale
.getISOCountries() // Fetch list of ISO 3166 country codes
.map { // Create a new Locale in users default language, but set country to X
it to Locale("", it).displayCountry // then extract the localized name of the country.
}
.toMap() // Turn into Map with ISO 3166 key and Localised country name as value
```

该 issue 提到了原始 XML 文件和 Kotlin Locale.getISOCountries().displayCountry 流程，但没有提到任何仓库文件或测试。请定位当前的地区名称数据和生成入口，然后将其与 Java Locale 的行为进行比较。完成的标准是选定一致同意的数据源，并更新国家名称生成，同时为现有用例进行验证。

由索引模型根据 Issue 内容生成。