Download the language file from osTicket.com or grab the one being used on your webserver.
How to extract files from .phar archives - Stack Over Flow
https://stackoverflow.com/questions/12997385/extracting-files-from-phar-archive
Search the contained files for the string that you want to edit. "Painel de Controlo do".
Edit the string to read how you want it to read.
Save the file.
Either re-phar the folder, or use the language pack un-phared on your webserver.