If there is a text added by a third-party plugin and it is not automatically translated, please make sure that the plugin has the pot file, then we can use a Translate plugin to translate the text you want.
For example, you can see the text below which has not been translated:
Please follow these steps to use the Loco Translate plugin to translate it.
Go to Loco Translate > Plugin > Select the plugin containing the text you want to translate
Select the language you want to translate
Select the text you want to translate and enter the translation string into the language input box
Save the file and check again with YayMail, you will see the translated text.