Is there any way to detect an RTL language in Java?

Question

I need to be able to detect whether the current language my user is viewing is an RTL (Right To Left) language like Arabic.

At the moment I'm just detecting this based on the language code from the system property user.language, but there must be a better way.

Answer 1

ComponentOrientation.getOrientation(new Locale(System.getProperty("user.language"))).isLeftToRight();  

• Resource

Answer 2

I felt a bit dirty relying on AWT classes which are quite dated and I was dealing with BCP-47 language codes, so I ended up copying this code from Google Closure Templates:

/**
 * A regular expression for matching right-to-left language codes.
 * See {@link #isRtlLanguage} for the design.
 */
private static final Pattern RtlLocalesRe = Pattern.compile(
    "^(ar|dv|he|iw|fa|nqo|ps|sd|ug|ur|yi|.*[-_](Arab|Hebr|Thaa|Nkoo|Tfng))" +
    "(?!.*[-_](Latn|Cyrl)($|-|_))($|-|_)");
/**
 * Check if a BCP 47 / III language code indicates an RTL language, i.e. either:
 * - a language code explicitly specifying one of the right-to-left scripts,
 *   e.g. "az-Arab", or<p>
 * - a language code specifying one of the languages normally written in a
 *   right-to-left script, e.g. "fa" (Farsi), except ones explicitly specifying
 *   Latin or Cyrillic script (which are the usual LTR alternatives).<p>
 * The list of right-to-left scripts appears in the 100-199 range in
 * http://www.unicode.org/iso15924/iso15924-num.html, of which Arabic and
 * Hebrew are by far the most widely used. We also recognize Thaana, N'Ko, and
 * Tifinagh, which also have significant modern usage. The rest (Syriac,
 * Samaritan, Mandaic, etc.) seem to have extremely limited or no modern usage
 * and are not recognized.
 * The languages usually written in a right-to-left script are taken as those
 * with Suppress-Script: Hebr|Arab|Thaa|Nkoo|Tfng  in
 * http://www.iana.org/assignments/language-subtag-registry,
 * as well as Sindhi (sd) and Uyghur (ug).
 * The presence of other subtags of the language code, e.g. regions like EG
 * (Egypt), is ignored.
 */
public static boolean isRtlLanguage(String languageString) {
  return languageString != null &&
      RtlLocalesRe.matcher(languageString).find();
}

See https://closure-templates.googlecode.com/svn-history/r21/trunk/java/src/com/google/template/soy/internal/i18n/BidiUtils.java