You shouldn’t be using a constant (in your case CORE_THEME_NAME) for the textdomain. This is because the call to __ is parsing your code, not running it. Simply said: it’s not looking up the value of the constant. So, it won’t translate. Quoting the famous Otto:
Inside all translation functions, no PHP variables are
allowed in the strings, for any reason, ever. Plain single-quoted
strings only.