Of course they can:
var’aq – Esolang. A programming language using Klingon vocabulary.
Of course, the pIqaD (see Klingon alphabets) does not have an official Unicode encoding: the ostensive reason is that Klingonists don’t actually use the pIqaD. The gossip is that the German arm of the ISO vetoed it, for fear of bringing Unicode into disrepute. (Then Unicode went and dumped every daft emoji they could find into the codeset; way to pick the wrong target, German arm of ISO.)
That means you would need to use an unofficial mapping into the Unicode Private Use area (ConScript Unicode Registry), if you want your var’aq program to show in pIqaD. But if you’re going to be programming in var’aq, I suggest the unofficialness of the ConScript Unicode Registry is the least of your problems…