Messages in the resource bundle should have format described in docs\api\java\text\MessageFormat.html

Within a String, "''" represents a single quote. A QuotedString can contain arbitrary characters except single quotes; the surrounding single quotes are removed. An UnquotedString can contain arbitrary characters except single quotes and left curly brackets. Thus, a string that should result in the formatted message "'{0}'" can be written as "'''{'0}''" or "'''{0}'''".

So a message "Can't find reader for {0} or file doesn't exist" should be stored as "Can''t find reader for {0} or file doesn''t exist"