The original text says Gehenna, not hell. Gehenna has been translated into hell in many bibles, but Jesus said Gehenna, which is/was a garbage dump outside of the city. If He had meant hell, He would've said hell. The jews probably knew the concept of hell from the pagan religions around them. But "hell" didn't exist in the jewish religion.
It's about punishment in the fire my friend.
Matthew 5:22 (NKJV)
22 But whoever says, 'You fool!' shall be in danger of hell fire.
Matthew 5:22 (ASV)
22 ; and whosoever shall say, Thou fool, shall be in danger of the hell of fire.
Matthew 5:22 (AMP)
22 , and whoever says, You cursed fool! [You empty-headed idiot!] shall be liable to and unable to escape the hell (Gehenna) of fire.
Matthew 5:22 (BBE)
22 ; and whoever says, You foolish one, will be in danger of the hell of fire.
Matthew 5:22 (MontgomeryNT)
22 , while he who curses his brother shall be liable to the Gehenna of Fire.
Matthew 5:22 (Darby)
22 ; but whosoever shall say, Fool, shall be subject to the penalty of the hell of fire.
Matthew 5:22 (ESV)
22 ; and whoever says, ‘You fool!’ will be liable to the hell of fire.
Matthew 5:22 (GW)
22 Whoever calls another believer a fool will answer for it in hellfire.
Matthew 5:22 (NASB)
22 "; and whoever says, 'You fool,' shall be guilty enough to go into the fiery hell.
Matthew 5:22 (NIV)
22 But anyone who says, 'You fool!' will be in danger of the fire of hell.
Matthew 5:22 (NLT)
22 And if you curse someone, you are in danger of the fires of hell.
Matthew 5:22 (NRSV)
22 ; and if you say, 'You fool,' you will be liable to the hell of fire.
Matthew 5:22 (TLB)
22 And if you curse him, you are in danger of the fires of hell.
Matthew 5:22 (WesleyNT)
22 ; but whosoever shall say, Thou fool, shall be liable to hell-fire.
Matthew 5:22 (WEY)
22 ; and that whoever says, 'You fool!' shall be liable to the Gehenna of Fire.
Matthew 5:22 (YLT)
22 , and whoever may say, Rebel! shall be in danger of the gehenna of the fire.