I already can program a little in PHP. All my websites are programmed in PHP. I was planning on learning a little about RoR and maybe code one of my websites in this language. But I was wondering, is it a good idea to learn another language besides PHP? Is it a good idea to have knowledge of several programming language? Or is it a good idea to use my time and learn PHP even better? I need some advise.
It is only a good idea if you would learn ruby's ins and outs first, before you attempt to learn and to use Rails.
Learning is always good.
If you have the time and feel atracted to it, you should do it!
In my experience Rails has a wider ecosystem of great tools to get a new application up and going quickly. I'd definitely recommend spending some time learning it. You'll at least, then, be in the position to know which language is best for individual applications.