Yes, there are APL programmers on SO (but not many!).
I think the answer is that there is no standard on this.
For a scalar solution, I use "pick":
x⊃f t
While for a Boolean array I use indexing as you do above:
f t[x]
I always use index origin zero, so there is no need to add 1, and the parens are not needed.
If these are not simple enough, I think you have to cover them with a function named "if". That will also let you put the true and false in the perhaps more natural ordering of t f.