Some audio workstation software has a de-clipping option. I've had very
limited success with it. There are lots of adjustments.
Most distortion adds harmonics, so there is no frequency band but the
harmonics are higher.
In general, there's not too much you can do. I'd try running it through the
Samplitude de-clipper for example (that's what I have), but I wouldn't
expect spectacular results.
I would also find this difficult because the language difference would make
it more difficult for me to assess the impact on intelligibility of any
modifications to the sound.
The simplest thing to do is to roll off the high end, that will make a
minor improvement, If you roll off too much, then intelligibility will suffer.
I'm assuming you cannot re-record this...