Things like emails sent to users by different plugins can not be translated because they do not appear in the front-end.
For these other types of content you can display content based on language using the shortcode:
[trp_language language="en_US"] English content only [/trp_language]
An important use case of the conditional shortcode is for translating images, basically displaying different images for different languages.
[trp_language language="en_US"] <img src="https://example.com/image_en.png" /> [/trp_language] [trp_language language="fr_FR"] <img src="https://example.com/image_fr.png" /> [/trp_language]