2001 diesel Jetta stopped all by herself while on high speed

I was driving on the highway in my 2001 jetta (332000 km) on the cruise control yesterday and suddenly it just started slowing down and stopped. Putting my feet in the gas did nothing . Before stopping completely the battery light came on. After won’t start anymore, just making a sound like it is trying but turn in the butter.
To be honest the check engine has been on for a while but we are pretty sure that is the glow plugs because it is a recurrent problem… Nothing else light up and there was no sound or smoke. Help? Can we salvage her?
Thank you!

What does “turn in the butter” mean?
When trying to start, does the engine crank over more slowly than normal? Or does it not turn over at all?

If butter means the motor is spinning faster than usual I have a dire guess that explains it and your motor stopping.

The timing belt snapped. Has this been changed in the last 40-50k miles?

I don’t know what turn in the butter means either. I hope you weren’t putting your feet IN the gas either.

All you said is that it spontaneously slowed and stopped. So did it actually stall? Was the battery light the ONLY light on? Up until that moment that is started slowing, was the car acting weird in any other ways?

And what Tony Carlos asked - better description of “won’t start.”

If I had to just make a complete WAG based only on this info, my WAG would be that your alternator died, and your battery gave up its last running the car that last little bit. When, exactly, in this sequence did the battery light come on?