Add test for GH #5780

Author: lb90

tests/std/test.lst

@@ -271,6 +271,7 @@ tests\GH_005472_do_not_overlap
 tests\GH_005546_containers_size_type_cast
 tests\GH_005553_regex_character_translation
 tests\GH_005768_pow_accuracy
+tests\GH_005780_non_ascii_locales
 tests\LWG2381_num_get_floating_point
 tests\LWG2510_tag_classes
 tests\LWG2597_complex_branch_cut

tests/std/tests/GH_005780_non_ascii_locales/env.lst

@@ -0,0 +1,4 @@
+# Copyright (c) Microsoft Corporation.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+RUNALL_INCLUDE ..\usual_matrix.lst

tests/std/tests/GH_005780_non_ascii_locales/test.cpp

@@ -0,0 +1,41 @@
+// Copyright (c) Microsoft Corporation.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include <algorithm>
+#include <cassert>
+#include <clocale>
+#include <iomanip>
+#include <iostream>
+#include <string>
+
+std::string set_locale(const std::string& locale_name) {
+    const char* ret = std::setlocale(LC_ALL, locale_name.c_str());
+    assert(ret != nullptr);
+    return ret;
+}
+
+std::string query_locale() {
+    const char* ret = std::setlocale(LC_ALL, nullptr);
+    assert(ret != nullptr);
+    return ret;
+}
+
+void assert_string_non_ascii(const std::string& string) {
+    const auto char_not_ascii = [](const char c) { return (c & 0x80) != 0; };
+    assert(std::any_of(string.begin(), string.end(), char_not_ascii));
+}
+
+void test_gh_5780() {
+    // https://learn.microsoft.com/en-us/cpp/c-runtime-library/language-strings#supported-language-strings
+    std::string locale_name = set_locale("norwegian-bokmal.437");
+    assert_string_non_ascii(locale_name);
+
+    std::cerr.imbue(std::locale::classic());
+    std::cerr << std::setprecision(2) << 0.1 << std::endl;
+
+    assert(query_locale() == locale_name);
+}
+
+int main() {
+    test_gh_5780();
+}