Index: lib/libc/locale/collate.c
===================================================================
--- lib/libc/locale/collate.c
+++ lib/libc/locale/collate.c
@@ -84,7 +84,8 @@
 void *
 __collate_load(const char *encoding, __unused locale_t unused)
 {
-	if (strcmp(encoding, "C") == 0 || strcmp(encoding, "POSIX") == 0) {
+	if (strcmp(encoding, "C") == 0 || strcmp(encoding, "POSIX") == 0 ||
+	    strncmp(encoding, "C.", 2) == 0) {
 		return &__xlocale_C_collate;
 	}
 	struct xlocale_collate *table = calloc(sizeof(struct xlocale_collate), 1);
@@ -122,7 +123,8 @@
 	table->__collate_load_error = 1;
 
 	/* 'encoding' must be already checked. */
-	if (strcmp(encoding, "C") == 0 || strcmp(encoding, "POSIX") == 0) {
+	if (strcmp(encoding, "C") == 0 || strcmp(encoding, "POSIX") == 0 ||
+	    strncmp(encoding, "C.", 2) == 0) {
 		return (_LDP_CACHE);
 	}
 
Index: lib/libc/locale/ldpart.c
===================================================================
--- lib/libc/locale/ldpart.c
+++ lib/libc/locale/ldpart.c
@@ -63,7 +63,8 @@
 	size_t		namesize, bufsize;
 
 	/* 'name' must be already checked. */
-	if (strcmp(name, "C") == 0 || strcmp(name, "POSIX") == 0) {
+	if (strcmp(name, "C") == 0 || strcmp(name, "POSIX") == 0 ||
+	    strncmp(name, "C.", 2) == 0) {
 		*using_locale = 0;
 		return (_LDP_CACHE);
 	}
Index: share/ctypedef/Makefile
===================================================================
--- share/ctypedef/Makefile
+++ share/ctypedef/Makefile
@@ -14,6 +14,7 @@
 	-f ${MAPLOC}/map.${.IMPSRC:T:R:E} \
 	-i ${.IMPSRC} ${.OBJDIR}/${.IMPSRC:T:R}  || true
 
+LOCALES+=	C.UTF-8
 LOCALES+=	be_BY.CP1131
 LOCALES+=	ca_IT.ISO8859-1
 LOCALES+=	ca_IT.ISO8859-15
@@ -21,7 +22,6 @@
 LOCALES+=	en_US.ISO8859-1
 LOCALES+=	en_US.ISO8859-15
 LOCALES+=	en_US.US-ASCII
-LOCALES+=	en_US.UTF-8
 LOCALES+=	hi_IN.ISCII-DEV
 LOCALES+=	hy_AM.ARMSCII-8
 LOCALES+=	ja_JP.SJIS
@@ -45,82 +45,83 @@
 
 
 
-SAME+=		en_US.UTF-8 ru_RU.UTF-8
-SAME+=		en_US.UTF-8 zh_TW.UTF-8
-SAME+=		en_US.UTF-8 zh_HK.UTF-8
-SAME+=		en_US.UTF-8 zh_CN.UTF-8
-SAME+=		en_US.UTF-8 uk_UA.UTF-8
-SAME+=		en_US.UTF-8 tr_TR.UTF-8
-SAME+=		en_US.UTF-8 sv_SE.UTF-8
-SAME+=		en_US.UTF-8 sv_FI.UTF-8
-SAME+=		en_US.UTF-8 sr_RS.UTF-8@latin
-SAME+=		en_US.UTF-8 sr_RS.UTF-8
-SAME+=		en_US.UTF-8 sl_SI.UTF-8
-SAME+=		en_US.UTF-8 sk_SK.UTF-8
-SAME+=		en_US.UTF-8 se_NO.UTF-8
-SAME+=		en_US.UTF-8 se_FI.UTF-8
-SAME+=		en_US.UTF-8 ro_RO.UTF-8
-SAME+=		en_US.UTF-8 pt_PT.UTF-8
-SAME+=		en_US.UTF-8 pt_BR.UTF-8
-SAME+=		en_US.UTF-8 pl_PL.UTF-8
-SAME+=		en_US.UTF-8 nn_NO.UTF-8
-SAME+=		en_US.UTF-8 nl_NL.UTF-8
-SAME+=		en_US.UTF-8 nl_BE.UTF-8
-SAME+=		en_US.UTF-8 nb_NO.UTF-8
-SAME+=		en_US.UTF-8 mn_MN.UTF-8
-SAME+=		en_US.UTF-8 lv_LV.UTF-8
-SAME+=		en_US.UTF-8 lt_LT.UTF-8
-SAME+=		en_US.UTF-8 ko_KR.UTF-8
-SAME+=		en_US.UTF-8 kk_KZ.UTF-8
-SAME+=		en_US.UTF-8 ja_JP.UTF-8
-SAME+=		en_US.UTF-8 it_IT.UTF-8
-SAME+=		en_US.UTF-8 it_CH.UTF-8
-SAME+=		en_US.UTF-8 is_IS.UTF-8
-SAME+=		en_US.UTF-8 hy_AM.UTF-8
-SAME+=		en_US.UTF-8 hu_HU.UTF-8
-SAME+=		en_US.UTF-8 hr_HR.UTF-8
-SAME+=		en_US.UTF-8 hi_IN.UTF-8
-SAME+=		en_US.UTF-8 he_IL.UTF-8
-SAME+=		en_US.UTF-8 fr_FR.UTF-8
-SAME+=		en_US.UTF-8 fr_CH.UTF-8
-SAME+=		en_US.UTF-8 fr_CA.UTF-8
-SAME+=		en_US.UTF-8 fr_BE.UTF-8
-SAME+=		en_US.UTF-8 fi_FI.UTF-8
-SAME+=		en_US.UTF-8 eu_ES.UTF-8
-SAME+=		en_US.UTF-8 et_EE.UTF-8
-SAME+=		en_US.UTF-8 es_MX.UTF-8
-SAME+=		en_US.UTF-8 es_ES.UTF-8
-SAME+=		en_US.UTF-8 es_CR.UTF-8
-SAME+=		en_US.UTF-8 es_AR.UTF-8
-SAME+=		en_US.UTF-8 en_ZA.UTF-8
-SAME+=		en_US.UTF-8 en_SG.UTF-8
-SAME+=		en_US.UTF-8 en_PH.UTF-8
-SAME+=		en_US.UTF-8 en_NZ.UTF-8
-SAME+=		en_US.UTF-8 en_IE.UTF-8
-SAME+=		en_US.UTF-8 en_HK.UTF-8
-SAME+=		en_US.UTF-8 en_GB.UTF-8
-SAME+=		en_US.UTF-8 en_CA.UTF-8
-SAME+=		en_US.UTF-8 en_AU.UTF-8
-SAME+=		en_US.UTF-8 el_GR.UTF-8
-SAME+=		en_US.UTF-8 de_DE.UTF-8
-SAME+=		en_US.UTF-8 de_CH.UTF-8
-SAME+=		en_US.UTF-8 de_AT.UTF-8
-SAME+=		en_US.UTF-8 da_DK.UTF-8
-SAME+=		en_US.UTF-8 cs_CZ.UTF-8
-SAME+=		en_US.UTF-8 ca_IT.UTF-8
-SAME+=		en_US.UTF-8 ca_FR.UTF-8
-SAME+=		en_US.UTF-8 ca_ES.UTF-8
-SAME+=		en_US.UTF-8 ca_AD.UTF-8
-SAME+=		en_US.UTF-8 bg_BG.UTF-8
-SAME+=		en_US.UTF-8 be_BY.UTF-8
-SAME+=		en_US.UTF-8 ar_SA.UTF-8
-SAME+=		en_US.UTF-8 ar_QA.UTF-8
-SAME+=		en_US.UTF-8 ar_MA.UTF-8
-SAME+=		en_US.UTF-8 ar_JO.UTF-8
-SAME+=		en_US.UTF-8 ar_EG.UTF-8
-SAME+=		en_US.UTF-8 ar_AE.UTF-8
-SAME+=		en_US.UTF-8 am_ET.UTF-8
-SAME+=		en_US.UTF-8 af_ZA.UTF-8
+SAME+=		C.UTF-8 en_US.UTF-8
+SAME+=		C.UTF-8 ru_RU.UTF-8
+SAME+=		C.UTF-8 zh_TW.UTF-8
+SAME+=		C.UTF-8 zh_HK.UTF-8
+SAME+=		C.UTF-8 zh_CN.UTF-8
+SAME+=		C.UTF-8 uk_UA.UTF-8
+SAME+=		C.UTF-8 tr_TR.UTF-8
+SAME+=		C.UTF-8 sv_SE.UTF-8
+SAME+=		C.UTF-8 sv_FI.UTF-8
+SAME+=		C.UTF-8 sr_RS.UTF-8@latin
+SAME+=		C.UTF-8 sr_RS.UTF-8
+SAME+=		C.UTF-8 sl_SI.UTF-8
+SAME+=		C.UTF-8 sk_SK.UTF-8
+SAME+=		C.UTF-8 se_NO.UTF-8
+SAME+=		C.UTF-8 se_FI.UTF-8
+SAME+=		C.UTF-8 ro_RO.UTF-8
+SAME+=		C.UTF-8 pt_PT.UTF-8
+SAME+=		C.UTF-8 pt_BR.UTF-8
+SAME+=		C.UTF-8 pl_PL.UTF-8
+SAME+=		C.UTF-8 nn_NO.UTF-8
+SAME+=		C.UTF-8 nl_NL.UTF-8
+SAME+=		C.UTF-8 nl_BE.UTF-8
+SAME+=		C.UTF-8 nb_NO.UTF-8
+SAME+=		C.UTF-8 mn_MN.UTF-8
+SAME+=		C.UTF-8 lv_LV.UTF-8
+SAME+=		C.UTF-8 lt_LT.UTF-8
+SAME+=		C.UTF-8 ko_KR.UTF-8
+SAME+=		C.UTF-8 kk_KZ.UTF-8
+SAME+=		C.UTF-8 ja_JP.UTF-8
+SAME+=		C.UTF-8 it_IT.UTF-8
+SAME+=		C.UTF-8 it_CH.UTF-8
+SAME+=		C.UTF-8 is_IS.UTF-8
+SAME+=		C.UTF-8 hy_AM.UTF-8
+SAME+=		C.UTF-8 hu_HU.UTF-8
+SAME+=		C.UTF-8 hr_HR.UTF-8
+SAME+=		C.UTF-8 hi_IN.UTF-8
+SAME+=		C.UTF-8 he_IL.UTF-8
+SAME+=		C.UTF-8 fr_FR.UTF-8
+SAME+=		C.UTF-8 fr_CH.UTF-8
+SAME+=		C.UTF-8 fr_CA.UTF-8
+SAME+=		C.UTF-8 fr_BE.UTF-8
+SAME+=		C.UTF-8 fi_FI.UTF-8
+SAME+=		C.UTF-8 eu_ES.UTF-8
+SAME+=		C.UTF-8 et_EE.UTF-8
+SAME+=		C.UTF-8 es_MX.UTF-8
+SAME+=		C.UTF-8 es_ES.UTF-8
+SAME+=		C.UTF-8 es_CR.UTF-8
+SAME+=		C.UTF-8 es_AR.UTF-8
+SAME+=		C.UTF-8 en_ZA.UTF-8
+SAME+=		C.UTF-8 en_SG.UTF-8
+SAME+=		C.UTF-8 en_PH.UTF-8
+SAME+=		C.UTF-8 en_NZ.UTF-8
+SAME+=		C.UTF-8 en_IE.UTF-8
+SAME+=		C.UTF-8 en_HK.UTF-8
+SAME+=		C.UTF-8 en_GB.UTF-8
+SAME+=		C.UTF-8 en_CA.UTF-8
+SAME+=		C.UTF-8 en_AU.UTF-8
+SAME+=		C.UTF-8 el_GR.UTF-8
+SAME+=		C.UTF-8 de_DE.UTF-8
+SAME+=		C.UTF-8 de_CH.UTF-8
+SAME+=		C.UTF-8 de_AT.UTF-8
+SAME+=		C.UTF-8 da_DK.UTF-8
+SAME+=		C.UTF-8 cs_CZ.UTF-8
+SAME+=		C.UTF-8 ca_IT.UTF-8
+SAME+=		C.UTF-8 ca_FR.UTF-8
+SAME+=		C.UTF-8 ca_ES.UTF-8
+SAME+=		C.UTF-8 ca_AD.UTF-8
+SAME+=		C.UTF-8 bg_BG.UTF-8
+SAME+=		C.UTF-8 be_BY.UTF-8
+SAME+=		C.UTF-8 ar_SA.UTF-8
+SAME+=		C.UTF-8 ar_QA.UTF-8
+SAME+=		C.UTF-8 ar_MA.UTF-8
+SAME+=		C.UTF-8 ar_JO.UTF-8
+SAME+=		C.UTF-8 ar_EG.UTF-8
+SAME+=		C.UTF-8 ar_AE.UTF-8
+SAME+=		C.UTF-8 am_ET.UTF-8
+SAME+=		C.UTF-8 af_ZA.UTF-8
 SAME+=		en_US.ISO8859-1 sv_SE.ISO8859-1
 SAME+=		en_US.ISO8859-1 sv_FI.ISO8859-1
 SAME+=		en_US.ISO8859-1 pt_PT.ISO8859-1
Index: tools/tools/locale/Makefile
===================================================================
--- tools/tools/locale/Makefile
+++ tools/tools/locale/Makefile
@@ -54,7 +54,7 @@
 .endif
 
 all:
-	cp ${ETCDIR}/common.UTF-8.src ${CLDRDIR}/posix/xx_Comm_US.UTF-8.src
+	cp ${ETCDIR}/common.UTF-8.src ${CLDRDIR}/posix/xx_Comm_C.UTF-8.src
 .for t in ${TYPES}
 .  if ${KNOWN:M${t}}
 	test -d ${t} || mkdir ${t}
@@ -105,7 +105,7 @@
 .endfor
 
 transfer-rollup:
-	cp ${ETCDIR}/common.UTF-8.src ${CLDRDIR}/posix/xx_Comm_US.UTF-8.src
+	cp ${ETCDIR}/common.UTF-8.src ${CLDRDIR}/posix/xx_Comm_C.UTF-8.src
 
 rollup:
 	perl -I tools tools/utf8-rollup.pl \
Index: tools/tools/locale/tools/cldr2def.pl
===================================================================
--- tools/tools/locale/tools/cldr2def.pl
+++ tools/tools/locale/tools/cldr2def.pl
@@ -416,6 +416,9 @@
 }
 
 sub transform_ctypes {
+	# Add the C.UTF-8
+	$languages{"C"}{"x"}{data}{"x"}{$DEFENCODING} = undef;
+
 	foreach my $l (sort keys(%languages)) {
 	foreach my $f (sort keys(%{$languages{$l}})) {
 	foreach my $c (sort keys(%{$languages{$l}{$f}{data}})) {
@@ -424,13 +427,12 @@
 		next if (defined $languages{$l}{$f}{definitions}
 		    && $languages{$l}{$f}{definitions} !~ /$TYPE/);
 		$languages{$l}{$f}{data}{$c}{$DEFENCODING} = 0;	# unread
-		my $file;
-		$file = $l . "_";
-		$file .= $f . "_" if ($f ne "x");
-		$file .= $c;
+		my $file = $l;
+		$file .= "_" . $f if ($f ne "x");
+		$file .= "_" . $c if ($c ne "x");
 		my $actfile = $file;
 
-		my $filename = "$CLDRDIR/posix/xx_Comm_US.UTF-8.src";
+		my $filename = "$CLDRDIR/posix/xx_Comm_C.UTF-8.src";
 		if (! -f $filename) {
 			print STDERR "Cannot open $filename\n";
 			next;
@@ -939,8 +941,8 @@
 				} keys(%{$hashtable{$hash}});
 		} elsif ($TYPE eq "ctypedef") {
 			@files = sort {
-				if ($a eq 'en_x_US.UTF-8') { return -1; }
-				elsif ($b eq 'en_x_US.UTF-8') { return 1; }
+				if ($a eq 'C_x_x.UTF-8') { return -1; }
+				elsif ($b eq 'C_x_x.UTF-8') { return 1; }
 				if ($a =~ /^en_x_US/) { return -1; }
 				elsif ($b =~ /^en_x_US/) { return 1; }
 
@@ -962,6 +964,7 @@
 		}
 		if ($#files > 0) {
 			my $link = shift(@files);
+			$link =~ s/_x_x//;	# special case for C
 			$link =~ s/_x_/_/;	# strip family if none there
 			foreach my $file (@files) {
 				my @a = split(/_/, $file);
@@ -987,9 +990,9 @@
 			next;
 		}
 		foreach my $e (sort keys(%{$languages{$l}{$f}{data}{$c}})) {
-			my $file = $l . "_";
-			$file .= $f . "_" if ($f ne "x");
-			$file .= $c;
+			my $file = $l;
+			$file .= "_" . $f if ($f ne "x");
+			$file .= "_" . $c if ($c ne "x");
 			next if (!defined $languages{$l}{$f}{data}{$c}{$e});
 			print FOUT "LOCALES+=\t$file.$e\n";
 		}