On the ruby tests at least, it calls 'permsol' where the actual tests and the code want "permute'. It might be nice if these were consistent.

I agree on the first part, but as a tranlator I felt obliged to respect the original author's will to keep it a tad easier and thus return a string instead of an error. No big deal anyway, if you ask me.

Imho handling extra spaces was not an issue, but I edited the code a bit so that now the random strings are generated without leading or trailing spaces.

Thanks for your feed :)

Not sure about other languages, but in ruby, the "Not a string" and "Not letters" return values, should probably throw an ArgumentError. Also, it wasn't obvious what was supposed to happen with blanks at the beginning and end of the phrase. You might want to mention that they should be stripped off (or at least that's what it took for me to get it to work).

Same thing here ... I added this test case
Test.assert_equals(prefill(0,1), [])
and it suceeds locally. This is with ruby. Any thoughts?