Index: include/xlocale/_string.h
===================================================================
--- include/xlocale/_string.h
+++ include/xlocale/_string.h
@@ -46,6 +46,7 @@
  * POSIX2008 functions
  */
 int	 strcoll_l(const char *, const char *, locale_t);
+char	*strerror_l(int num, locale_t);
 size_t	 strxfrm_l(char *, const char *, size_t, locale_t);
 #endif /* _XLOCALE_STRING1_H */
 
Index: lib/libc/include/libc_private.h
===================================================================
--- lib/libc/include/libc_private.h
+++ lib/libc/include/libc_private.h
@@ -431,4 +431,9 @@
 
 void __throw_constraint_handler_s(const char * restrict msg, int error);
 
+struct __nl_cat_d;
+struct _xlocale;
+struct __nl_cat_d *__catopen_l(const char *name, int type,
+	    struct _xlocale *locale);
+
 #endif /* _LIBC_PRIVATE_H_ */
Index: lib/libc/nls/msgcat.c
===================================================================
--- lib/libc/nls/msgcat.c
+++ lib/libc/nls/msgcat.c
@@ -58,6 +58,7 @@
 #include "un-namespace.h"
 
 #include "../locale/xlocale_private.h"
+#include "libc_private.h"
 
 #define _DEFAULT_NLS_PATH "/usr/share/nls/%L/%N.cat:/usr/share/nls/%N/%L:"	\
 				_PATH_LOCALBASE "/share/nls/%L/%N.cat:"		\
@@ -121,6 +122,12 @@
 
 nl_catd
 catopen(const char *name, int type)
+{
+	return (__catopen_l(name, type, __get_locale()));
+}
+
+nl_catd
+__catopen_l(const char *name, int type, locale_t locale)
 {
 	struct stat sbuf;
 	struct catentry *np;
@@ -139,7 +146,7 @@
 		lang = NULL;
 	else {
 		if (type == NL_CAT_LOCALE)
-			lang = querylocale(LC_MESSAGES_MASK, __get_locale());
+			lang = querylocale(LC_MESSAGES_MASK, locale);
 		else
 			lang = getenv("LANG");
 
Index: lib/libc/string/Symbol.map
===================================================================
--- lib/libc/string/Symbol.map
+++ lib/libc/string/Symbol.map
@@ -110,6 +110,10 @@
 	timingsafe_memcmp;
 };
 
+FBSD_1.6 {
+	strerror_l;
+};
+
 FBSDprivate_1.0 {
 	__strtok_r;
 };
Index: lib/libc/string/strerror.3
===================================================================
--- lib/libc/string/strerror.3
+++ lib/libc/string/strerror.3
@@ -32,12 +32,13 @@
 .\"     @(#)strerror.3	8.1 (Berkeley) 6/9/93
 .\" $FreeBSD$
 .\"
-.Dd April 5, 2011
+.Dd December 7, 2020
 .Dt STRERROR 3
 .Os
 .Sh NAME
 .Nm perror ,
 .Nm strerror ,
+.Nm strerror_l ,
 .Nm strerror_r ,
 .Nm sys_errlist ,
 .Nm sys_nerr
@@ -53,12 +54,15 @@
 .In string.h
 .Ft "char *"
 .Fn strerror "int errnum"
+.Ft "char *"
+.Fn strerror_l "int errnum" "locale_t"
 .Ft int
 .Fn strerror_r "int errnum" "char *strerrbuf" "size_t buflen"
 .Sh DESCRIPTION
 The
 .Fn strerror ,
-.Fn strerror_r
+.Fn strerror_l ,
+.Fn strerror_r ,
 and
 .Fn perror
 functions look up the error message string corresponding to an
@@ -68,8 +72,17 @@
 .Fn strerror
 function accepts an error number argument
 .Fa errnum
-and returns a pointer to the corresponding
-message string.
+and returns a pointer to the corresponding message string in the current locale.
+The function is not thread-safe, it returns pointer to the buffer the could
+be overwritten by a call to
+.Fn strerror
+from other thread.
+.Pp
+The
+.Fn strerror_l
+takes an error number and locale arguments and return string,
+corresponding to specified error, in the requested locale.
+The function is thread-safe.
 .Pp
 The
 .Fn strerror_r
Index: lib/libc/string/strerror.c
===================================================================
--- lib/libc/string/strerror.c
+++ lib/libc/string/strerror.c
@@ -45,6 +45,8 @@
 #include <stdio.h>
 
 #include "errlst.h"
+#include "../locale/xlocale_private.h"
+#include "libc_private.h"
 
 /*
  * Define buffer big enough to contain delimiter (": ", 2 bytes),
@@ -78,34 +80,35 @@
 	strlcat(buf, t, len);
 }
 
-int
-strerror_r(int errnum, char *strerrbuf, size_t buflen)
+static int
+strerror_rl(int errnum, char *strerrbuf, size_t buflen, locale_t locale)
 {
 	int retval = 0;
 #if defined(NLS)
 	int saved_errno = errno;
 	nl_catd catd;
-	catd = catopen("libc", NL_CAT_LOCALE);
+
+	catd = __catopen_l("libc", NL_CAT_LOCALE, locale);
 #endif
 
 	if (errnum < 0 || errnum >= __hidden_sys_nerr) {
 		errstr(errnum,
 #if defined(NLS)
-			catgets(catd, 1, 0xffff, __uprefix),
+		    catgets(catd, 1, 0xffff, __uprefix),
 #else
-		        __uprefix,
+		    __uprefix,
 #endif
-			strerrbuf, buflen);
+		   strerrbuf, buflen);
 		retval = EINVAL;
 	} else {
 		if (strlcpy(strerrbuf,
 #if defined(NLS)
-			catgets(catd, 1, errnum, __hidden_sys_errlist[errnum]),
+		    catgets(catd, 1, errnum, __hidden_sys_errlist[errnum]),
 #else
-			__hidden_sys_errlist[errnum],
+		    __hidden_sys_errlist[errnum],
 #endif
-			buflen) >= buflen)
-		retval = ERANGE;
+		    buflen) >= buflen)
+			retval = ERANGE;
 	}
 
 #if defined(NLS)
@@ -116,12 +119,33 @@
 	return (retval);
 }
 
+int
+strerror_r(int errnum, char *strerrbuf, size_t buflen)
+{
+	return (strerror_rl(errnum, strerrbuf, buflen, __get_locale()));
+}
+
+char *
+strerror_l(int num, locale_t locale)
+{
+#ifndef __NO_TLS
+	static _Thread_local char ebuf[NL_TEXTMAX];
+
+	if (strerror_rl(num, ebuf, sizeof(ebuf), __get_locale()) != 0)
+		errno = EINVAL;
+	return (ebuf);
+#else
+	errno = ENOTSUP;
+	return (NULL);
+#endif
+}
+
 char *
 strerror(int num)
 {
 	static char ebuf[NL_TEXTMAX];
 
-	if (strerror_r(num, ebuf, sizeof(ebuf)) != 0)
+	if (strerror_rl(num, ebuf, sizeof(ebuf), __get_locale()) != 0)
 		errno = EINVAL;
 	return (ebuf);
 }