Linux – Command or option for the xgettext, msginit, msgfmt sequence for setting the MIME type

msgfmt “invalid multibyte sequence” error on a Polish text is corrected by manually editing the MIME Content-Type charset in the template file. Is there some command or option for the xgettext, msginit, msgfmt sequence for setting the MIME type?

cat >plt.cxx <<EOF
// plt.cxx
#include <libintl.h>
#include <locale.h>
#include <iostream>
int main (){
    setlocale(LC_ALL, "");
    bindtextdomain("plt", ".");
    textdomain( "plt");
    std::cout << gettext("Invalid input. Enter a string at least 20 characters long.") << std::endl;
}
EOF
g++ -o plt plt.cxx
xgettext --package-name plt --package-version 1.2 --default-domain plt --output plt.pot plt.cxx
sed --in-place plt.pot --expression='s/CHARSET/UTF-8/'
msginit --no-translator --locale pl_PL --output-file plt_polish.po --input plt.pot
sed --in-place plt_polish.po --expression='/#: /,$ s/""/"Nieprawidłowo wprowadzone dane. Wprowadź ciąg przynajmniej 20 znaków."/'
mkdir --parents ./pl_PL.utf8/LC_MESSAGES
msgfmt --check --verbose --output-file ./pl_PL.utf8/LC_MESSAGES/plt.mo plt_polish.po
LANGUAGE=pl_PL.utf8 ./plt