perldelta for locale changes

pod/perldelta.pod

@@ -415,6 +415,46 @@ Don't clear the integer flag C<IOK> from lines in the C<<
 @{"_<$sourcefile"} >> array when a C<dbstate> op is removed for that
 line.  This was broken when fixing [GH #19198].  [GH #21564]
 
+=item *
+
+Many bug fixes have been made for using locales under threads and in
+embedded perls.  And workarounds for libc bugs have been added.  As a
+result thread-safe locale handling is now the default under OpenBSD, and
+MingW when compiled with UCRT.
+
+However, testing has shown that Darwin's implementation of thread-safe
+locale handling has bugs.  So now Perl doesn't attempt to use the
+thread-safe operations when compiled on Darwin.
+
+As before, you can check to see if your program is running with
+thread-safe locales by checking if the value of C<${^SAFE_LOCALES}> is
+1.
+
+=item *
+
+Various bugs have been fixed when perl is configured with
+C<-Accflags=-DNO_LOCALE_NUMERIC> or any other locale category (or
+categories).
+
+=item *
+
+Not all locale categories need be set to the same locale.  Perl now
+works around bugs in the libc implementations of locale handling on some
+platforms that previously could result in mojibake.
+
+=item *
+
+C<LC_ALL> is represented in one of two ways when not all locale
+categories are set to the same locale.  On some platforms, such as Linux
+and Windows, the representation is of the form of a series of
+C<'category=locale-name'> pairs.  On other platforms, such as *BSD, the
+representation is positional like S<C<I<name1> / I<name2> / ... >>.
+I<name1> is always for a particular category as defined by the platform,
+as are the other names.  The sequence that separates the names
+(the S<C< / >> above) also varies by platform.  Previously, perl had
+problems with platforms that used the positional notation.  This is now
+fixed.
+
 =back
 
 =head1 Known Problems