Source?
The only thing in AL law related to pistols that I remember is that the barrel must be under 12".  It doesn't say anything about overall length.

So an Encore w/ a 15" barrel as a handgun is a no go? Or is it treated like a long gun? Or does it not meet the definition of anything!

My take is that it would not qualify as a pistol for things such as concealed carry.  You could own it, shoot it,...  You just couldn't carry it under your jacket.

If it is over 26” does that mean it is considered a firearm and you can put a vertical foregrip on it?

Federally yes, because it is considered a firearm at that point.  Alabama law defines a pistol as having a barrel length of less than 12 inches.

Alabama isn't as clear on their definitions of all the configurations of different firearms.  Here are three definitions:

13A-11-62

(2) RIFLE. Any weapon designed or redesigned, made or remade, and intended to be fired from the shoulder and designed or redesigned and made or remade to use the energy of the explosive in a fixed metallic cartridge to fire only a single projectile through a rifled bore for each pull of the trigger.

(4) SHORT-BARRELED RIFLE. A rifle having one or more barrels less than 16 inches in length and any weapon made from a rifle (whether by alteration, modification, or otherwise) if such weapon, as modified, has an overall length of less than 26 inches.

13A-11-70

(1) PISTOL. Any firearm with a barrel less than 12 inches in length.

One could interpret the rifle definition as any shouldering of a firearm making it a rifle, regardless of it having a brace or a stock.  As long as it doesn't violate federal law the state isn't going to really care I don't think:

13A-11-63

(a) A person who possesses, obtains, receives, sells, or uses a short-barreled rifle or a short-barreled shotgun in violation of federal law is guilty of a Class C felony.

So no a clear definition of a firearm with an OAL of over 26" and a VFG.