I also sent this already directly to Joey, but later found this bug report. My take is this:
--- /usr/bin/ts 2019-02-20 22:03:31.000000000 +0100 +++ ./ts 2023-03-01 21:06:41.177886024 +0100 @@ -53,6 +53,7 @@ use strict; use POSIX q{strftime}; no warnings 'utf8'; +use open q{:locale}; $|=1; This should ensure that the I/O is treated with the encoding indicated by the locale, be it UTF-8 or something else. Alrighty then, Thomas