I recently tried to import a long set of keywords (about 4000 terms). i set up the file in excel and then tried to import the records. I kept getting this message:
only text files encoded with ascii or unicode UTF-8 are supported when importing keywords.
I finally tracked down the problem when i converted the file to a MS word text file, broke it down into parts and eventually found the problem record. for some reason, the apostrophe in the words "don't know" had been corrupted to a weird character. after i corrected this, everything worked.
however, this took a long time. It would have been helpful if lightroom could have at least pinpointed the line where the import failed or offered to convert non-compliant charaters to some specific character or set of characters.