test(libSceSystemService): cover resolving the host language from an injected source

Checks the first recognised locale wins over later and earlier unrecognised
ones, malformed entries are skipped, and an unrecognised or missing locale
returns English (United States) with exactly one notice that names the first
detected locale or says the host reports none.

core/libs/tests/SystemServiceLanguageLocale.cpp

@@ -262,6 +262,33 @@ void RequirePosixSource() {
     Require(Posix({{"LC_ALL", "C"}, {"LANG", "de_DE"}}) == Locales{"C"}, "LC_ALL=C overrides LANG");
 }
 
+int Resolve(const std::vector<std::string>& locales, std::vector<std::string>& notices) {
+    return SystemServiceLocale::ResolveHostLanguage([&locales] { return locales; }, [&notices](const std::string& line) { notices.push_back(line); });
+}
+
+void RequireHostResolution() {
+    using namespace SystemServiceLocale;
+    std::vector<std::string> notices;
+    Require(Resolve({"de_DE.UTF-8"}, notices) == German && notices.empty(), "one recognised locale");
+    Require(Resolve({"pt_BR"}, notices) == PortugueseBrazil && notices.empty(), "pt_BR");
+    Require(Resolve({"lt", "uk", "fr"}, notices) == Ukrainian && notices.empty(), "first recognised entry wins");
+    Require(Resolve({"es", "fr", "de_DE.UTF-8"}, notices) == Spanish && notices.empty(), "LANGUAGE order");
+    Require(Resolve({"en-GB", "fr"}, notices) == EnglishUk && notices.empty(), "first entry before later ones");
+    Require(Resolve({"zh-Hant-TW"}, notices) == ChineseTraditional && notices.empty(), "zh-Hant-TW");
+    Require(Resolve({"lt_LT.UTF-8"}, notices) == EnglishUs && notices.size() == 1, "unlisted language");
+    Require(notices[0] == "ANYPS5_LANGUAGE=auto: the host locale \"lt_LT.UTF-8\" has no console language, using English (United States), language number 1", notices[0]);
+    notices.clear();
+    Require(Resolve({"C"}, notices) == EnglishUs && notices.size() == 1, "C");
+    Require(notices[0].find("\"C\"") != std::string::npos && notices[0].find("English (United States)") != std::string::npos, notices[0]);
+    notices.clear();
+    Require(Resolve({"lt", "lv"}, notices) == EnglishUs && notices.size() == 1 && notices[0].find("\"lt\"") != std::string::npos, "first unrecognised entry is named");
+    notices.clear();
+    Require(Resolve({}, notices) == EnglishUs && notices.size() == 1, "no locale");
+    Require(notices[0] == "ANYPS5_LANGUAGE=auto: the host reports no locale, using English (United States), language number 1", notices[0]);
+    notices.clear();
+    Require(Resolve({"garbage!", "ja_JP"}, notices) == Japanese && notices.empty(), "malformed entry is skipped");
+}
+
 }
 
 int main() {
@@ -276,4 +303,5 @@ int main() {
     RequireOtherRows();
     RequireFallbackRules();
     RequirePosixSource();
+    RequireHostResolution();
 }