The Gantt Chart in Jaspersoft - Widget Pro does not render the special characters for any language other than English.
The Gantt chart is rendered correctly in the preview section, but when exported as PDF/PPT the special characters get rendered as escaped unicode values e.g. \u0107 -> "ć"
Clarity PPM 16.x
This issue has been reported to Tibco as JSS-3050
(Tibco Jaspersoft) - open for Gantt chart where it does not support localization.
Tibco has targeted this to be fixed in Jaspersoft 9.1.