By reading and understanding the guidelines. There isn't now - and hasn't been for quite a while - a general ban on interpreters.

Relevant sections of the (current Feb 2016) guidelines : 2.7 Apps that download code in any way or form will be rejected 2.8 Apps that install or launch other executable code will be rejected[0]

There are a bunch of interpreters in the store for various languages. The only problem is if you download arbitrary code. In theory anyway. In reality the review process is indistinguishable from arbitrary and capricious.

[0]https://developer.apple.com/app-store/review/guidelines/#fun...