It’s one thing to build a demonstration aircraft another to turn that into a production fighter aircraft.
Take the Mitsubishi X-2 Shinshin for example.
You need a combination of both the airframe, Engines and essential systems. Fifth generation aircraft are loaded with more information systems and integration of systems that on previous generations were podded on or operated as bolt on or without regard to the degrees of information technology.
Defensive aides, electronic warfare, offensive and defensive radar, optical targeting and designation, LPOI communications, traditional communications, low observable aircraft coatings and fabrication of materials, weapons and munitions management. Internal and external stores. Fuel management, flight systems, cooling, pilot displays both cockpit and head mounted, Power management, missile launch warning and more. Development, production and procurement has itself to be managed so has to allow it all to be installed in your finished product in time for delivery. Plus it all has to fit perfectly inside your mold lines. No nip and tuck later. because fixing that is like trying to squeeze a new piece inside a 3D puzzle.
Well Erdogan has seemingly managed to achieve demonstrating new vehicles and had some success in a number of projects. It’s in the Major components where they have not seemingly had as much luck. The Altay engine soap opera in example. Maybe they can pull it off. Maybe but it’s an uphill struggle. That’s why they’re so few countries building modern fighter jets. The industrial complex needed for highly sophisticated modern weapons is much higher than it was before.