aspell cannot find dictionary even though I've installed it

[vapnik spaknik]

I need to update my recoll index, and recoll needs aspell, and aspell needs 
en.dat, but can't find it:

Error: The language "en" is not known. This is probably because: the file 
"/gnu/store/zrmhnj3pwchn2msphgnwzwd3q89m46rn-aspell-0.60.8/lib/aspell-0.60/en.dat"
 can not be opened for reading.

So I installed aspell-dict-en, which contains en.dat, but aspell still can't 
find it. I even tried reinstalling aspell, but that didn't change anything.
Seems like this is a bug, or am I doing something wrong?