I solved by myself, maybe. In the constructor of TextEdit, after textEdit = new QTextEdit(this); add QTextCodec::setCodecForLocale(QTextCodec::codecForName("UTF-8")); then I could save .md file as encoded by UTF-8. Without this, .md file will be saves as shift-jis (system's default). .txt files are always saved using UTF-8 encoding without the added line.