I thought is was Danish accent.
From Bristleback's lines:
That barkeep got us into this, we'll get ourselves out.
Let's put our differences behind us. What do you say?
Tusk, let's partner up on this one.
Look, we can all fight each other once the killing is done.
Looks like it's you and me, Tusk.
Between your tusks and mine, they won't know what hit em.
No need for a rematch.
Your tusks were no match for mine.
You had it coming, Tusk.
I been waiting to do that.
Ah, now I feel better.
Wasn't a draw that time.
Well, that's the end of that.
Looks like I won the next round.
Bristleback seems fairly obviously Tusk's rival from this.
His accent is very thick, it seems eastern european, possibly romanian, ukranian or bulgarian. I think boxing is popular there that's probably why.
He is fighting for a beer? Really? (read this in the same voice Anti Mage uses when he uses the Blink Dagger response)
Interesting that it is one of the only lores that explain how the concerned heroes got into the Ancient's war.
On a complete side note, I want to see a Brewmaster,Tusk and Bristlebog lineup eventually^^
Everyone has a story.
For a list of all fan lores of unreleased heroes, http://dev.dota2.com/showthread.php?t=37955.
On a side side note, the only tiny itsy bitsy problem with Tusk's lore is that it doesn't even hint at how he's able to create ice barriers or giant snowballs, but that can easily be solved through the ability flavor texts.