Visa for internship in ireland

I am approved as a good candidate for a position in Ireland but they do not want to wait more than 2 months to hire somebody for the position. I offered them to start as an internship if it takes shorter to take visa for an intenship.I do not want to miss that position. I will be happy if somebody help me...
What kind of visa do i need for internship and how long it takes to take it?
what is fast-track work authorization and how long does it take for an employer to get one for a foreigner?

Thank you