That's really not necessary and nothing to worry about, dnsmasq simply ignores these lines and jumps to the next line to read in.
And as long as there are foreign characters in certain hosts files, this remains the case as the blocking_file is renewed once every week on update day.
Removing the offending character from a domain name may have a detrimental effect:
appl<illigal char>e.com
after removing:
apple.com
Hmmm.
You could look for a way to filter those files, converting these entries into punycode.