cat "multibyte or wide character" error

[Snoopy]

first, dont open up new threads for questions which are  popping up after recieving an answer in another thread, use the old one

second, one possible answer is already given by sort

Code:

Set LC_ALL='C' to work around the problem.

never the less, there is another great linux tool called iconv

Code:

iconv -c input.txt > output.txt
or
iconv -c -t=UTF-8 input.txt > output.txt

this will strip unprintable chars from input, but never the less, it seems your input files are malformed or have been through some seriuos misconversion between different character encodings which will mostly result in these problems you mentioned