Concat task with in-line string may fail, e.g.: <property name="fileContent" value="ÄÖÜ äöü ß"/> <concat destfile="output-wrong.txt" outputencoding="iso-8859-15">${fileContent}</concat> The encoding of concat task (default: null) will not forwarded to embedded StringResource (default encoding: UTF-8; formerly: null). It only works when encoding attributes of Concat task and StringResource matches. Workaround: <property name="fileContent" value="ÄÖÜ äöü ß"/> <concat destfile="output-fixed.txt" encoding="utf8" outputencoding="iso-8859-15"> <string encoding="utf8">${fileContent}</string> </concat> -> use explizit StringResource and define matching encoding values for <concat> and <string>.