No need to learn Bahasa, English is generally the spoken language when flying with Air Asia. They will occasionally revert back to Bahasa, but if you ask them nicely to speak English for the sake of good CRM they will do so.
Europeans are made very welcome there - esp by the easy on the eye female cabin crew.
If you make the effort to learn some of their language it will be appreciated by the locals.
Worked there a few years ago and really enjoyed my time there.
While there the DCA would not validate under 25's for some reason - might have changed since, but worth checking out as people taking money from you may not tell you until too late for you.
Validation can take up to 2-3 months and they need you to be in the country on a tourist visa while waiting, so you might have to pop up to Phuket and pop back in on a new visa while waiting. The problem is that the DCA don't validate without a work permit, but they might have fast tracked this by now.
This money to fly thing is nothing new, while I was there they used Eagle Jet "pay to fly pilots", but stop as they were not happy with the quality.