I found this way
IContext context;
try {
context = com.webmethods.portal.bizPolicy.impl.ContextFactory.acquireContext(true);
context.setLocale(getMedicineContextInfo().getUserGMEDLocale().getSessionLocale());
FacesContext.getCurrentInstance().getViewRoot().setLocale(getMedicineContextInfo().getUserGMEDLocale().getSessionLocale());
} catch (PortalException e) {
e.printStackTrace();
}
However this only stores the Locale in the current session.
The set in the viewRoot is required to defined the locale for th current request.
#webMethods-BPMS#MWS-CAF-Task-Engine#webMethods