Strings added using the “BEAF - Ultimate Before After Image Slider & Gallery” plugin are not translatable. The words are defined in the Dashboard in the settings of each gallery: https://snipboard.io/7ruezo.jpg
Solution:
1- Set the sliders post type to translatable
2- Duplicate the sliders to English
3- Edit the duplicated English slider to change the before and after strings
4- Update the English sliders
5- Use the English Sliders shortcode on the English page
