Using with v1.3.5 Linux and as per this Tutorial:
https://www.zen-cart.com/tutorials/index.php?article=36
Modifying the default Language File - /includes/languages/english.php

Example: You need to modify the title, so that instead of reading Zen Cart!, it reads Your Store Name!

Make a directory with the same name as your template name in /includes/languages, so you now have /includes/languages/custom.

Copy english.php to this directory.

Then, you can make any needed modifications in your new:
/includes/languages/custom/english.php
The above does not seem to be correct. Following the instructions only gave errors.
Seems the 'english.php' must stay where it is.

Maybe not a bug but perhaps, information that was specific to previous versions?