I want to make some simple language changes but can't locate the files.
For example, the message that says "Sorry, you don't have permission to access this area."

In this particular case, the site has 2.3.2b and CBB 3.08. I want to change the message received by anonymous users who try to access the forum.

Are there general rules about where the language files are located or an easy means to find them? Subtle changes to these files are the final touches to customization in my mind, but I'm finding it challenging.

Is there a guide?

Any advice appreciated as always.

generally language files are located under the "languages" directory either for the whole website in the website root, or under the modules/yourmodule folder. As in regard to the You don't have permissions error message I believe you can change it in module/system/language/english/

good luck

Yev

Thanks.

After much searching, I found it in mysite/language/english/global.php. I too thought it would be associated to the system folder, but no.

A list of most language files (will be incomplete in the future) is here.