Kimberly (Alexi's wife) told me he likes improv lyrics (i.e. gibberish) and that all lyrics not listed are nonsense with random words thrown in. I don't think she was entirely correct, though, because some songs obviously have lyrics that aren't printed (Towards Dead End, Children of Bodom, Mask of Sanity, parts of other songs, etc.).
I believe Something Wild has little to no gibberish... Aleix said in an interview that there were problems and only one song's lyrics were written down because of time constraints (they recorded it all in one week), but he would've copied them all down.
The bottom line for HB and FtR is that if the lyrics aren't printed, there is a fair amount of improv in that song, but I'm positive none of them are all improv.
