For lexicographic ordering comm(1) compares chars without specified signedness. So, when 'char' is 'signed char', comm assumes that UTF-8 multibyte units appear before ASCII. Must force unsigned comparison to ensure compatibility with sort(1) beyond 7 bits. Test:
	comm <{echo Bar; echo Bär} <{echo Bär; echo Foo}

Reference: /n/sources/patch/comm-utf-sort
Date: Wed Aug 30 18:19:27 CES 2017
Signed-off-by: antox@ml.lv

--- /sys/src/cmd/comm.c	Wed Aug 30 18:19:04 2017
+++ /sys/src/cmd/comm.c	Wed Aug 30 18:19:01 2017
@@ -156,7 +156,7 @@
 		a++;
 		b++;
 	}
-	if(*a < *b)
+	if((uchar)*a < (uchar)*b)
 		return 1;
 	return 2;
 }