8269513: Clarify the spec wrt useOldISOCodes system property

Reviewed-by: lancea, bpb, iris, joehw

Author: naotoj

src/java.base/share/classes/java/util/Locale.java

@@ -455,9 +455,11 @@
  *
  * <p>For the backward compatible behavior, the system property
  * {@systemProperty java.locale.useOldISOCodes} reverts the behavior
- * back to prior to Java SE 17 one. If the system property is set
- * to {@code true}, those three current language codes are mapped to their
- * backward compatible forms.
+ * back to that of before Java SE 17. If the system property is set to
+ * {@code true}, those three current language codes are mapped to their
+ * backward compatible forms. The property is only read at Java runtime
+ * startup and subsequent calls to {@code System.setProperty()} will
+ * have no effect.
  *
  * <p>The APIs added in 1.7 map between the old and new language codes,
  * maintaining the mapped codes internal to Locale (so that