1. You can use the default code in functions.php of the child theme instead of the one from the previous post.
2. If you want to overwrite responsive styles you need use @media element in style.css in the child theme folder. Please describe the issues with more details. What exactly can’t be overwritten?
3. Sorry, but translation files must be located in the parent theme as they are loaded from there. Those files won’t be effective in the child theme.
4. To change color of sprite icons you need edit the picture with some image editor.
