I've dabbled in APL, and a couple of jobs ago I worked extensively in kdb/q. I found it to be an immensely powerful tool in its natural environment of time-series processing, and extraordinarily painful to use outside that domain. Typically I'd write the core logic in q with a small wrapper in Java or Python to do string formatting and other tasks that kdb falls down on.

Which is fine. Not every language needs to do everything. Horses for courses.