There are translations that simplify its meaning to "is". But I would like to find better translations. It might be "it is meant to be" or something like that, but I'm not sure which translation is better.
I think the best translation is It's about. For example: Se trata de como mejorar tu español = It's about how to improve your spanish.
fuonk, about your question you can say treat in case of medical terms. For example: Este paciente se trata con aspirinas y reposo. This pacient is treated with aspirins and rest.
That wasn't my question; my question was whether "tratar" and "treat" are cognates. In English, "concern an issue" = "be about an issue" = "treat an issue", although "treat" is the least commonly used of these. I was just trying to make a connection between "tratarse" and "be about" via the cognate "treat", if it is indeed a cognate.
@fuonk: Yes, they are cognates. Both "treat" and "tratar" have their roots in the Latin "trahere".
"is about" is certainly one of the most frequent meanings. It all depends on the context. Here's an overview of what "tratar" can mean: http://spanish.about.com/od/usingparticularverbs/a/tratar.htm
Yes, they are definitely cognates tratar and treat (Don't treat me like a fool / No me trates como un tonto).
The link from christian is super-helpful, but it doesn't clearly indicate why "it is" is a possible translation, as in the original question. I can't help you, but just today I wrote an email saying something like "Please print me the file Exam.doc, and the file Chapter1.pdf, which IS a text we will use on the exam." To do so, I wrote "Favor de imprimir el archivo Exam.doc y el archivo hapter1.doc, que SE TRATA de un texto que es parte del examen." Hope it helps.
@christian: Thank you for a good resource! Actually I was looking for a particular form of tratar: "se trata de ..." And from what I have found in this resource - "tratar de, tratarse de, to speak about, to have as a subject" and there are some examples. For translation of my example (posted above) I would probably choose this variation. "Speaking about Cthulhu Tech, it is a game inspired by the myths of H.P. Lovecraft but adapted to near future." May be this is not the best translation, but it is Ok for me.