Here is how to convert text files from one character encoding to another in GNU/Linux:
iconv -f ASCII -t UTF-8//IGNORE file.txt -o output.txt
iconv -f ISO-8859-1 -t UTF-8//TRANSLIT file.txt output.txt
The -f parameter denotes “from” and -t parameter denotes “to” character set.
//IGNORE means the “iconv” will ignore any characters that are not available in the target character set.
While “//TRANSLIT” means the converter will attempt to substitute characters that are not available in the target character set to the closest characters available, failing that, “???” will be replaced in its place.
Most GNU/Linux distribution have iconv preinstalled, if not, please consult your distribution documentation.