Well, I suppose there are two ways to be 'good at processing text'. The first way is to quickly and efficiently let the user do what they want, which is how Python approaches the problem, eg, str[0:len(str)-1] + "'\''". I've only learned python in the last 12 months, and I need access to a lot less documentation than I need in elisp to write that.
The second way is to have a model that is so strong that it is worth the user learning that model (this is a rarer approach, but is more common in the lisp families - Clojure, for example, does this with variables). If elisp has this, it would be a good idea for someone to mention that in the documentation, because I don't recall ever seeing anyone say "Wow! This elisp model of processing text is amazing! I've been doing it wrong my whole life!". I have seen variants of "which is not at all bad, but is very foreign".
I don't know of a best language, but manipulating text strings is the foundation of most web serving. So I'd say that the popular languages for that (python, perl, php, etc) are quite a bit better than elisp at processing text.