I didn't ask about your /includes/languages/ content. I asked about your /includes/templates/ content.
When creating a customized template, you FIRST start with creating a template folder under /includes/templates/YOUR_CHOSEN_TEMPLATE_FOLDERNAME_HERE/
Then when you customize language files, you take the same added name and create a folder of that same name under the /includes/languages/english/ folder, like /includes/languages/english/YOUR_CHOSEN_TEMPLATE_FOLDERNAME_HERE/ and put your customized files in there.
In the case of templates and languages, once you have the override foldername in place, you copy the originals (just the ones you intend to change) into that folder and make changes there.
In the paragraphs I just wrote above, the "override" foldername is represented by "YOUR_CHOSEN_TEMPLATE_FOLDERNAME_HERE". It could be called "fred" or "personalized" or "red_and_yellow_shoes" or "supercalifragilisticexpialidocious", etc. Pick a name and be consistent. You'll see built-in examples of a foldername called "classic", and you can (and should) follow that pattern.
There are several FAQ articles explaining how the template-override system works in great detail.
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