Poedit is free to use and free to download.
It’s created by WordPress, there is no need to pay for the premium features.
For translation, you will need this tool to translate the po file and it will save into mo file which is to be read by machine. There is no way for translation to work if you do not use a tool or plugin.
You should also keep a copy of the po or mo file for future update.
If you prefer to directly edit the Theme file, you can open up contact.php and make the edits. But it will be gone after theme update and you will have to do it again.