Throw IllegalArgumentException when unknown language tag is used in set_language

Author: hmusum

linguistics/src/main/java/com/yahoo/language/LocaleFactory.java

@@ -1,6 +1,7 @@
 // Copyright Vespa.ai. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
 package com.yahoo.language;
 
+import java.util.IllformedLocaleException;
 import java.util.Locale;
 import java.util.Objects;
 
@@ -45,7 +46,11 @@ public static Locale fromLanguageTag(String tag) {
             }
         }
         if (language.isEmpty()) return UNKNOWN;
-        return new Locale.Builder().setLanguage(language).setScript(script).setRegion(region).build();
+        try {
+            return new Locale.Builder().setLanguage(language).setScript(script).setRegion(region).build();
+        } catch (IllformedLocaleException e) {
+            throw new IllegalArgumentException("Unknown language tag '" + tag + "', it must be a language tag corresponding to RFC5646");
+        }
     }
 
 }

linguistics/src/test/java/com/yahoo/language/LocaleFactoryTestCase.java

@@ -6,6 +6,7 @@
 import java.util.Locale;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertThrows;
 import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.fail;
 
@@ -41,6 +42,11 @@ public void requireThatLocaleCanBeCreatedFromLanguageTag() {
         assertLocale("", "", "", "");
         assertLocale("z-foo", "", "", "");
         assertLocale("ojeroierhoiherohjdadsfodsfoifiopeoipefwoipfwe", "", "", "");
+
+        var exception = assertThrows(IllegalArgumentException.class,
+                                     () -> LocaleFactory.fromLanguageTag("foo-13"));
+        assertEquals("Unknown language tag 'foo-13', it must be a language tag corresponding to RFC5646",
+                     exception.getMessage());
     }
 
     private static void assertLocale(String tag, String language, String variant, String country) {