Move getLanguageSelfName to tools.h

This is a general utility which other ports can get use of.
Added tests

test/languageTools.cpp

@@ -0,0 +1,41 @@
+/*
+ * Copyright (C) 2023 Nikhil Tanwar (2002nikhiltanwar@gmail.com)
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * is provided AS IS, WITHOUT ANY WARRANTY; without even the implied
+ * warranty of MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, and
+ * NON-INFRINGEMENT.  See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
+ *
+ */
+
+#include "gtest/gtest.h"
+#include "../include/tools.h"
+
+namespace
+{
+
+TEST(LanguageToolsTest, englishTest)
+{
+    EXPECT_EQ(kiwix::getLanguageSelfName("eng"), "English");
+}
+
+TEST(LanguageToolsTest, manualValuesTest)
+{
+    EXPECT_EQ(kiwix::getLanguageSelfName("dty"), "डोटेली");
+}
+
+TEST(LanguageToolsTest, emptyStringTest)
+{
+    EXPECT_EQ(kiwix::getLanguageSelfName(""), "Undetermined");
+}
+
+}

test/meson.build

@@ -6,6 +6,7 @@ tests = [
     'pathTools',
     'otherTools',
     'opdsParsingTools',
+    'languageTools',
     'kiwixserve',
     'book',
     'manager',