Thank you, Amandeep, for your reply.
The initial problem was trying to see if the supplied utilities would be able to read and display the data as added to the file by some other program.
As I am rather new to metadata and metadata in PNG files in particular - for various other reasons I am stuck with PNG - and because I have yet to find a metadata editor which pretty well handles all possible metadata - not just the ones the programs originators thought suitable in their own opinion and their own preferences or needs - I wanted to learn about where the programs I was considering were putting the data from the fields they make available on ther front end.
As for the suitability of these utilities, I expected that they would handle all fields provided for by the standard - I believe to have been set by Adobe - in the way provided for by that standard and clearly the handling of the iTXt packed seems to be not according to the standard, which, as I understand it, calls for the strings to be encoded in UTF-8.