Configuring an editor for various languages using Factory Method Pattern
I need to know if my code is a valid implementation of the factory method pattern. 


No.

The reason is that the factory cannot be part of the objects to be created. I think you would be surprised to find a factory in the the hedge of your car, wouldn't you?

Generally spoken your approach fails the Separation of Concerns principle.

You have two responsibilities in your code that belong to a factory: 


identifying the requested type.
creating the actual object.


Both should be in a separate factory class.



Also: your "factory" is producing the wrong type of objects because of your misconception of inheritance.

We employ inheritance when the child classes differ in behavior. But your Editor extensions only differ in configuration (as far as your code example is showing...).

So what your (yet to build) factory should do is creating the "language depended"  key word list and pass that into a new instance of the one and only Editor class.