How to I get the IETF BCP47 Language code in Android API < 21

Question

Is there a clever way to get the BCP47 language code in Android for APIs less than 21? In API level 21+ the Locale.toLanguageTag is exactly what I need. How would you get this in lower API levels?

Answer 1

The good people of Apache Cordova developed a solution for this, as seen here.

I modified there code into the following solution:

/**
 * Modified from:
 * https://github.com/apache/cordova-plugin-globalization/blob/master/src/android/Globalization.java
 * 
 * Returns a well-formed ITEF BCP 47 language tag representing this locale string
 * identifier for the client's current locale
 *
 * @return String: The BCP 47 language tag for the current locale
 */
public static String toBcp47Language(Locale loc) {
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
        return loc.toLanguageTag();
    }

    // we will use a dash as per BCP 47
    final char SEP = '-';
    String language = loc.getLanguage();
    String region = loc.getCountry();
    String variant = loc.getVariant();

    // special case for Norwegian Nynorsk since "NY" cannot be a variant as per BCP 47
    // this goes before the string matching since "NY" wont pass the variant checks
    if (language.equals("no") && region.equals("NO") && variant.equals("NY")) {
        language = "nn";
        region = "NO";
        variant = "";
    }

    if (language.isEmpty() || !language.matches("\\p{Alpha}{2,8}")) {
        language = "und";       // Follow the Locale#toLanguageTag() implementation
        // which says to return "und" for Undetermined
    } else if (language.equals("iw")) {
        language = "he";        // correct deprecated "Hebrew"
    } else if (language.equals("in")) {
        language = "id";        // correct deprecated "Indonesian"
    } else if (language.equals("ji")) {
        language = "yi";        // correct deprecated "Yiddish"
    }

    // ensure valid country code, if not well formed, it's omitted
    if (!region.matches("\\p{Alpha}{2}|\\p{Digit}{3}")) {
        region = "";
    }

    // variant subtags that begin with a letter must be at least 5 characters long
    if (!variant.matches("\\p{Alnum}{5,8}|\\p{Digit}\\p{Alnum}{3}")) {
        variant = "";
    }

    StringBuilder bcp47Tag = new StringBuilder(language);
    if (!region.isEmpty()) {
        bcp47Tag.append(SEP).append(region);
    }
    if (!variant.isEmpty()) {
        bcp47Tag.append(SEP).append(variant);
    }

    return bcp47Tag.toString();
}