No supported languages are defined on manifest.xml

When I exported a project I saw these warnings:

WARNING: manifest.xml: No supported languages are defined. Language-specific resources will be ignored unless language support is added to the manifest file.

I wonder if I should add English to the xml (as that is the language I use in my strings under resources/) or doing that would have an unintended effect on the users? I do not have resources-eng/ folder.

I feel like this warning shouldn't be displayed in my case, because there are no language-specific resource folders and it should only be displayed if there is a "new" language folder that the developer forgot to add to the manifest.