Please explain me how to convert these old PHP site into responsive one. The address of site is www.cnc4milling.com. Will be very thankfull to receive an information or code which to implement and convert the site into responsive. The other problem is changing of language on the web. At the beginning the website was created with one language English, but was prepared to be with two languages, but it was not finished at all. Please let to solve these problems and to make it with changing language. I have created also bulgarian varinat of the web pages and need only code to implement and to be possible to change the languages. Will be very thankfull to receive competitive help.
Thank you in advance.
P.S. Sending css file of the web site.