Thank you jbadams.

One last question.

Is it possible to have a game engine without scripting language and add scripting language later on?

and is it possible to change scripting language from xxx to xxx?

I think it's possible but i need someone to confirm this.

Thanks

I'd say it would be possible to expose all functionality of the engine to a scripting language after the engine has been finished as that's simply a matter of writing the required interfacing code.

The problem would be that you would need a way to insert script execution to the main loop of the engine. Or you would have to move the main loop to the scripting language.

This could however pose a security risk. Normally the engine has the scripts running in a sandbox-like environment so scripts cannot harm the end-user or crash the entire application when a single script crashes. I do not know how good various scripting languages are at calling code in a sandbox-like environment. If they are not good at it, you have a huge security risk.

So it is possible depending on your definition of 'adding a scripting language to an engine without a scripting language', this is possible.