Add LocaleUtils.isLanguageUndetermined(Locale)

src/changes/changes.xml

@@ -59,6 +59,7 @@ The <action> type attribute can be add,update,fix,remove.
     <action                   type="add" dev="aherbert" due-to="Dan Watson">Add syntax for optional tokens to DurationFormatUtils #1062.</action>
     <action                   type="add" dev="ggregory" due-to="Gary Gregory">Add ArrayFill.</action>
     <action                   type="add" dev="ggregory" due-to="Gary Gregory">Add FastDateParser.TimeZoneStrategy.TzInfo.toString().</action>
+    <action                   type="add" dev="ggregory" due-to="Gary Gregory">Add LocaleUtils.isLanguageUndetermined(Locale).</action>
     <!-- UPDATE -->
     <action                   type="update" dev="ggregory" due-to="Gary Gregory">Bump commons-parent from 58 to 59.</action>
   </release>

src/main/java/org/apache/commons/lang3/LocaleUtils.java

@@ -38,7 +38,9 @@ import java.util.stream.Collectors;
  * @since 2.2
  */
 public class LocaleUtils {
+
     private static final char UNDERSCORE = '_';
+    private static final String UNDETERMINED = "und";
     private static final char DASH = '-';
 
     // class to avoid synchronization (Init on demand)
@@ -140,6 +142,22 @@ public class LocaleUtils {
         return StringUtils.isAllLowerCase(str) && (str.length() == 2 || str.length() == 3);
     }
 
+    /**
+     * Tests whether a Locale's language is undetermined.
+     * <p>
+     * A Locale's language tag is undetermined if it's value is {@code "und"}. If a language is empty, or not well-formed (for example, "a" or"e2"), it will be
+     * equal to {@code "und"}.
+     * </p>
+     *
+     * @param locale the locale to test.
+     * @return whether a Locale's language is undetermined.
+     * @see Locale#toLanguageTag()
+     * @since 3.14.0
+     */
+    public static boolean isLanguageUndetermined(final Locale locale) {
+        return locale == null || UNDETERMINED.equals(locale.toLanguageTag());
+    }
+
     /**
      * Checks whether the given String is a UN M.49 numeric area code.
      *

src/test/java/org/apache/commons/lang3/LocaleUtilsTest.java

@@ -19,6 +19,7 @@ package org.apache.commons.lang3;
 import static org.apache.commons.lang3.JavaVersion.JAVA_1_4;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNotEquals;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertSame;
@@ -359,6 +360,22 @@ public class LocaleUtilsTest extends AbstractLangTest {
         assertEquals(set.contains(LOCALE_QQ_ZZ), LocaleUtils.isAvailableLocale(LOCALE_QQ_ZZ));
     }
 
+    @Test
+    public void testIsLanguageUndetermined() {
+        final Set<Locale> set = LocaleUtils.availableLocaleSet();
+        // Determined
+        assertNotEquals(set.contains(LOCALE_EN), LocaleUtils.isLanguageUndetermined(LOCALE_EN));
+        assertNotEquals(set.contains(LOCALE_EN_US), LocaleUtils.isLanguageUndetermined(LOCALE_EN_US));
+        assertNotEquals(set.contains(LOCALE_FR), LocaleUtils.isLanguageUndetermined(LOCALE_FR));
+        assertNotEquals(set.contains(LOCALE_FR_CA), LocaleUtils.isLanguageUndetermined(LOCALE_FR_CA));
+        // Undetermined
+        assertEquals(set.contains(LOCALE_EN_US_ZZZZ), LocaleUtils.isLanguageUndetermined(LOCALE_EN_US_ZZZZ));
+        assertEquals(set.contains(LOCALE_QQ), LocaleUtils.isLanguageUndetermined(LOCALE_QQ));
+        assertEquals(set.contains(LOCALE_QQ_ZZ), LocaleUtils.isLanguageUndetermined(LOCALE_QQ_ZZ));
+        //
+        assertTrue(LocaleUtils.isLanguageUndetermined(null));
+    }
+
     /**
      * Test for 3-chars locale, further details at LANG-915
      *