Persitent bug – not able to translate email subject and heading

This is for the order payment recieve email. I didn’t check the others yet. I used the default string until now and saw that the subject wasn’t translated, but the heading was. After that I edited those strings and translated them in the PL string section. After that whether the subject and not the heading got translated anymore.

I entered the translated string in both languages (just two languages on the website) in the PL string settings. Still not showing the translated strings. I reverted the settings in the email settings tab (used the default string) and it couldn’t go back to prior state. Now heading and subject are not translated even with the default string. Can anyone help as this is nuts?