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diff --git a/gl/m4/locale-en.m4 b/gl/m4/locale-en.m4
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+# locale-en.m4
+# serial 1
+dnl Copyright (C) 2003-2025 Free Software Foundation, Inc.
+dnl This file is free software; the Free Software Foundation
+dnl gives unlimited permission to copy and/or distribute it,
+dnl with or without modifications, as long as this notice is preserved.
+dnl This file is offered as-is, without any warranty.
+
+dnl From Bruno Haible.
+
+dnl Determine the name of an English (or American English) locale with
+dnl UTF-8 encoding.
+AC_DEFUN_ONCE([gt_LOCALE_EN_UTF8],
+[
+  AC_REQUIRE([AC_CANONICAL_HOST])
+  AC_REQUIRE([AM_LANGINFO_CODESET])
+  AC_CACHE_CHECK([for an english Unicode locale], [gt_cv_locale_en_utf8], [
+    case "$host_os" in
+      *-musl* | midipix*)
+        dnl On musl libc, all kinds of ll_CC.UTF-8 locales exist, even without
+        dnl any locale file on disk. But they are effectively equivalent to the
+        dnl C.UTF-8 locale, except for locale categories (such as LC_MESSSAGES)
+        dnl for which localizations (.mo files) have been installed.
+        gt_cv_locale_en_utf8=en_US.UTF-8
+        ;;
+      *)
+        AC_LANG_CONFTEST([AC_LANG_SOURCE([[
+#include <locale.h>
+#include <time.h>
+#if HAVE_LANGINFO_CODESET
+# include <langinfo.h>
+#endif
+#include <stdlib.h>
+#include <string.h>
+struct tm t;
+char buf[16];
+int main () {
+  /* On BeOS and Haiku, locales are not implemented in libc.  Rather, libintl
+     imitates locale dependent behaviour by looking at the environment
+     variables, and all locales use the UTF-8 encoding.  */
+#if !(defined __BEOS__ || defined __HAIKU__)
+  /* Check whether the given locale name is recognized by the system.  */
+# if defined _WIN32 && !defined __CYGWIN__
+  /* On native Windows, setlocale(category, "") looks at the system settings,
+     not at the environment variables.  Also, when an encoding suffix such
+     as ".65001" or ".54936" is specified, it succeeds but sets the LC_CTYPE
+     category of the locale to "C".  */
+  if (setlocale (LC_ALL, getenv ("LC_ALL")) == NULL
+      || strcmp (setlocale (LC_CTYPE, NULL), "C") == 0)
+    return 1;
+# else
+  if (setlocale (LC_ALL, "") == NULL) return 1;
+# endif
+  /* Check whether nl_langinfo(CODESET) is "UTF-8" or equivalent.  */
+# if HAVE_LANGINFO_CODESET
+  {
+    const char *cs = nl_langinfo (CODESET);
+    if (!(strcmp (cs, "UTF-8") == 0 || strcmp (cs, "UTF8") == 0
+          || strcmp (cs, "utf-8") == 0 || strcmp (cs, "utf8") == 0))
+      return 1;
+  }
+# endif
+# ifdef __CYGWIN__
+  /* On Cygwin, avoid locale names without encoding suffix, because the
+     locale_charset() function relies on the encoding suffix.  Note that
+     LC_ALL is set on the command line.  */
+  if (strchr (getenv ("LC_ALL"), '.') == NULL) return 1;
+# endif
+  /* Check the third month name.  */
+  t.tm_year = 1975 - 1900; t.tm_mon = 3 - 1; t.tm_mday = 24;
+  if (strftime (buf, sizeof (buf), "%B", &t) < 5 || strcmp (buf, "March") != 0)
+    return 1;
+#endif
+#if !defined __BIONIC__ /* Bionic libc's 'struct lconv' is just a dummy.  */
+  /* Check whether the decimal separator is a dot.  */
+  if (localeconv () ->decimal_point[0] != '.') return 1;
+#endif
+  return 0;
+}
+          ]])])
+        if AC_TRY_EVAL([ac_link]) && test -s conftest$ac_exeext; then
+          case "$host_os" in
+            # Handle native Windows specially, because there setlocale() interprets
+            # "ar" or "ara" as "Arabic" or "Arabic_Saudi Arabia.1256",
+            # "en" or "eng" as "English" or "English_United States.1252",
+            # "fr" or "fra" as "French" or "French_France.1252",
+            # "ge"(!) or "deu"(!) as "German" or "German_Germany.1252",
+            # "ja" or "jpn" as "Japanese" or "Japanese_Japan.932",
+            # and similar.
+            mingw* | windows*)
+              # Test for the hypothetical native Windows locale name.
+              if (LC_ALL='English_United States.65001' LC_TIME= LC_CTYPE= ./conftest; exit) 2>/dev/null; then
+                gt_cv_locale_en_utf8='English_United States.65001'
+              else
+                # None found.
+                gt_cv_locale_en_utf8=none
+              fi
+              ;;
+            *)
+              # Setting LC_ALL is not enough. Need to set LC_TIME to empty, because
+              # otherwise on Mac OS X 10.3.5 the LC_TIME=C from the beginning of the
+              # configure script would override the LC_ALL setting. Likewise for
+              # LC_CTYPE, which is also set at the beginning of the configure script.
+              # Test for the locale name with explicit encoding suffix first
+              # (this is necessary on Haiku).
+              if (LC_ALL=en_US.UTF-8 LC_TIME= LC_CTYPE= ./conftest; exit) 2>/dev/null; then
+                gt_cv_locale_en_utf8=en_US.UTF-8
+              else
+                # Test for the locale name without encoding suffix.
+                if (LC_ALL=en_US LC_TIME= LC_CTYPE= ./conftest; exit) 2>/dev/null; then
+                  gt_cv_locale_en_utf8=en_US
+                else
+                  # Test for the Solaris 10 locale name.
+                  if (LC_ALL=en.UTF-8 LC_TIME= LC_CTYPE= ./conftest; exit) 2>/dev/null; then
+                    gt_cv_locale_en_utf8=en.UTF-8
+                  else
+                    # None found.
+                    gt_cv_locale_en_utf8=none
+                  fi
+                fi
+              fi
+              ;;
+          esac
+        fi
+        rm -fr conftest*
+        ;;
+    esac
+  ])
+  LOCALE_EN_UTF8="$gt_cv_locale_en_utf8"
+  case "$LOCALE_EN_UTF8" in #(
+    '' | *[[\"\$\'*@<:@]]*)
+      dnl The empty value occurs when the conftest.c program above could not
+      dnl be compiled.  The other values might cause trouble with sh or make.
+      AC_MSG_WARN([invalid locale "$LOCALE_EN_UTF8"; assuming "none"])
+      LOCALE_EN_UTF8=none;;
+  esac
+  AC_SUBST([LOCALE_EN_UTF8])
+])