Sometime, you download file from Internet specially file that in local language which not encode with UTF-8 that unreadable on OSX. Your should guess what encode that file using and convert it in to UTF-8.
# convert tis-620 to utf-8 encoding $iconv -f tis-620 -t utf-8 source.xml > destination.xml
Example. Thai language on Windows system normally encode with TIS-620 when open it in OSX that will display with some symbol char that unreadable. You should convert that file from tis-620 to utf-8 which make it readable on osx.