private String localeToEmoji(Locale locale) {
    String countryCode = locale.getCountry();
    int firstLetter = Character.codePointAt(countryCode, 0) - 0x41 + 0x1F1E6;
    int secondLetter = Character.codePointAt(countryCode, 1) - 0x41 + 0x1F1E6;
    return new String(Character.toChars(firstLetter)) + new String(Character.toChars(secondLetter));

}

这里0x41表示大写字母A，0x1F1E6是Unicode表中的REGIONAL INDICATOR SYMBOL LETTER A，并且用户再次使用toUpper，这可能会导致问题

@Piyush更新回答：（请注意，我的代码要求国家代码大写）
build.gradle：

implementation 'androidx.emoji:emoji-bundled:1.1.0'
    implementation 'androidx.emoji:emoji:1.1.0'

countryToEmojiCode：

object CountryHelper {
    private const val flagsAsciiOffset = 127397
    fun countryToEmojiCode(countryCode: String) = StringBuilder().apply {
        val simCountryIso = if (countryCode == "UK") {
            "GB"
        } else {
            countryCode
        }
        simCountryIso.forEach {
            appendCodePoint(it.toInt() + flagsAsciiOffset)
        }
    }.toString()
}

用法：

val emojiInitializer = EmojiCompat.init(BundledEmojiCompatConfig(requireContext()))

emojiInitializer.registerInitCallback(
        EmojiCompatHelper { initialised: Boolean ->
            if (initialised) {
                val flagEmoji = EmojiCompat.get().process(flagEmojiCode).toString()
            }
        })

表情库的初始化程序回调：

class EmojiCompatHelper(private val initialised: (Boolean) -> Unit): EmojiCompat.InitCallback() {
    override fun onInitialized() {
        super.onInitialized()
        initialised(true)
    }

    override fun onFailed(throwable: Throwable?) {
        super.onFailed(throwable)
        initialised(false)
    }
}

使用Kotlin函数将country code转换为Flag表情符号。

fun countryFlag(code: String) = code
  .uppercase()
  .split("")
  .filter { it.isNotBlank() }
  .map { it.codePointAt(0) + 0x1F1A5 }
  .joinToString("") { String(Character.toChars(it)) }

println(countryFlag("in"))
// output 🇮🇳

添加扩展名：

fun String.toFlagEmoji(): String {
        // 1. It first checks if the string consists of only 2 characters: ISO 3166-1 alpha-2 two-letter country codes (https://en.wikipedia.org/wiki/Regional_Indicator_Symbol).
        if (this.length != 2) {
            return this
        }
    
        val countryCodeCaps =
            this.uppercase() // upper case is important because we are calculating offset
        val firstLetter = Character.codePointAt(countryCodeCaps, 0) - 0x41 + 0x1F1E6
        val secondLetter = Character.codePointAt(countryCodeCaps, 1) - 0x41 + 0x1F1E6
    
        // 2. It then checks if both characters are alphabet
        if (!countryCodeCaps[0].isLetter() || !countryCodeCaps[1].isLetter()) {
            return this
        }
    
        return String(Character.toChars(firstLetter)) + String(Character.toChars(secondLetter))
    }

这样命名它：

holder.countryFlag.text = countryCode.iso2.toFlagEmoji()