Revamped language system right away again to allow plugins to use it

plugins/builtin/source/lang/en_US.cpp

@@ -0,0 +1,13 @@
+#include <hex/plugin.hpp>
+
+namespace hex::plugin::builtin {
+
+    void registerLanguageEnUS() {
+        ContentRegistry::Language::registerLanguage("English (US)", "en-US");
+
+        ContentRegistry::Language::addLocalizations("en-US", {
+
+        });
+    }
+
+}