Forgive in advance as I am not a language art major.

In 3.0 You needed a +1 modifier to cast a lv one spell Arcane/divine it didn't matter. I've been looking all over, and I may be wording it wrong, but cant find Shit. So to the point does this same rule apply in 5th edition.

Over on the bg3 forums their saying a a barbarian with one lv wizard with a 8 intel will be able to cast spells. I know play your way let them play theirs. Ok. It just breaks my heart to see a great game I grew up with just have rules hacked so bad. 

Not in 5e as long as you know/prepared the spell and have the appropriate spell slot level or higher you can cast the spell. Having a low spell casting modifier will make it harder to pass the attack roll and/or the enemies will pass the saving throw more likely. 

Thank you optimistic14,

You can kind of think of it like a wizard swinging a greatsword to make a weapon attack. Technically, they can do it, but they’ll be really bad at it, to the point of why bother? It might not matter if you’re casting a spell to buff someone, so there’s no save or attack roll, but most of the time it will pretty much suck. 
Also, you can’t cast while raging, so if you want to spend a round buffing, to rage on round 2, when the whole fight will take usually 3-4 rounds, it might not be the best way to spend your time. 
Again, you can do it, but probably after the second or third time, you’ll realize it’s a poor choice. 

Bg3 (Baldur's gate 3) they are removing the multi class restrictions.  I have resigned myself to really not caring so much what others do as its not a pvp game, Ill stick to the way I choose to play. I was just curious if you could even do what I was describing.

Technically, your ability modifier is irrelevant, so long as you have the class and appropriate level, you're good to go. In terms of multiclassing, you have to have at least a 13, which equates to a minimum of...+1 to your modifier (before modifications). However, if you had an 8 (-1) Intelligence, you could start as a Wizard and still cast spells, so the difference isn't academic. Of course, you still can't multiclass because you need to have Intelligence of at least 13 to multiclass out of being a Wizard, but still...