The World-Ready Composer is a start but you'll also need a plug-in in you need to compose right-to-left paragraphs and not just phrases.
Here is a link to a plug-in that would help:
Directly? No. You need to hire a translator to do translation work. Once the text is translated you can import it back into ID.
There are many ways that a translation workflow can be set up, and some are better than others. I expect that our resident translation workflow expert, Joel Cherney, will weigh in with advice and questions once he wakes up.
Peter is correct, and probably read your question more accurately. You DO need a good translation workflow, AND you need to have a plug-in like the one from inTools.
Or if you have a subscription to the cloud you can install the ME/NA version of ID...
I have a project coming up where I need to translate English into Arabic.
I am guessing that you mean "I need to have English text translated into Arabic, by a literate human being who speaks Arabic as a first language who is familiar professionally with the subject matter, and proofread by a second similar human being, and I need to be able to lay it out in InDesign." If that's not what you mean - if you want to select English text in ID, then right-click on it and select something like "Translate," then you're going to be disappointed. Not only is there no such functionality in InDesign, but at the current state of the art there is no way to reliably get a translation that can be
easily read, grammatically correct and understood by people in the Middle-East who speak Arabic.
without using human beings. I've seen some surprisingly good machine translation in the EN<->AR language pair recently, completely free of humans, but it's still not up to the standards you specify. I don't know if it will ever be so.
Is this at all possible using InDesign?
Absolutely. Steve and Peter point out the two different ways you could use ID in this project - either with the official Middle Eastern version of ID, or with a plugin that turns on the hidden right-to-left and complex-script tools that are buried in your presumably plain-vanilla English install of InDesign.
However, if you're not already literate in Arabic yourself, or at least familiar with the special rules that govern Arabic typesetting (rules pretty much completely unlike the rules to which I assume you are accustomed in English) then there is very little chance that you will be able to lay out a document that will be easily read and free of layout-induced grammatical errors. If you are going to lay it out yourself (as opposed to jobbing it out to a designer who works in-language) then your best bet would be to study up first, and then have the translator review your layout work once you were finished. For what it's worth, I usually only handle Arabic myself when the requirement is that it be legible - if it needs to look good in any way, we work with some translators who also have some DTP expertise and who can work directly within InDesign.
All that being said - if you tell us more about your project, we can help you figure out the best way to complete it.