Merge pull request #55803 from nextcloud/bugfix/55274/dont-fallback-from-3letter-languages-to-2letter

fix(l10n): Don't fallback from 3-letter languages to 2-letter

lib/private/L10N/Factory.php

@@ -496,7 +496,7 @@ class Factory implements IFactory {
 
 				// Fallback from de_De to de
 				foreach ($available as $available_language) {
-					if (substr($preferred_language, 0, 2) === $available_language) {
+					if ($preferred_language_parts[0] === $available_language) {
 						return $available_language;
 					}
 				}

tests/lib/L10N/FactoryTest.php

@@ -351,6 +351,12 @@ class FactoryTest extends TestCase {
 			[null, 'de,en', ['ru', 'en'], 'en'],
 			[null, 'de-DE,en-US;q=0.8,en;q=0.6', ['ru', 'en'], 'en'],
 
+			// Don't fall back from kab (Kabyle) to ka (Georgian) - Unless specifically requested
+			[null, 'kab;q=0.8,en;q=0.6', ['ka', 'en'], 'en'],
+			[null, 'kab;q=0.8,de;q=0.6', ['ka', 'en', 'de'], 'de'],
+			[null, 'kab;q=0.8,de;q=0.7,ka;q=0.6', ['ka', 'en', 'de'], 'de'],
+			[null, 'kab;q=0.8,ka;q=0.7,de;q=0.6', ['ka', 'en', 'de'], 'ka'],
+
 			// Language for app
 			['files_pdfviewer', 'de', ['de'], 'de'],
 			['files_pdfviewer', 'de,en', ['de'], 'de'],