8371339: Illegal pattern char 'B' with locale.providers as HOST on macOS for Taiwanese

Reviewed-by: jlu, rriggs

src/java.base/macosx/classes/sun/util/locale/provider/HostLocaleProviderAdapterImpl.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2012, 2022, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2012, 2025, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -874,6 +874,17 @@ public class HostLocaleProviderAdapterImpl {
             sb.append('\'');
             break;
 
+        case 'B':
+            // 'B' character (day period) is not supported by SimpleDateFormat,
+            // this is a workaround in which 'B' character
+            // appearing in macos' pattern string (based on LDML) is replaced
+            // with 'a' character and hence resolved with am/pm strings.
+            // This workaround is based on the fallback mechanism
+            // specified in LDML spec for 'B' character, when a locale
+            // does not have data for day period ('B')
+            appendN('a', count, sb);
+            break;
+
         default:
             appendN(cldrLetter, count, sb);
             break;