Lots of Irish standard tunes has been successfully adopted by US roots musicicians and made into a vital part of their style.
Fiddle style
But since you're here, you're probably not interested in how to get an Irish tune to sound like bluegrass, but rather how to get a five string banjo to sound "Irish."The "fiddle style" usually associated with "authentic" Irisg solo banjo is a bit trickier on the five-stringed banjo. It can be done, but it takes some effort and there'll always be some limitations.
The three most important points are:
- Forget all you know about banjo technique
Ireland and USA may be just an ocean apart physically, but when it comes to banjo playing technique, they are separated by several universes. If you have some mandolin or guitar flatpicking experience, you're much better off using that as the basis for your "Irish" banjo style. - Get a flatpick.
There's no way to get the Irish sound or those fast triplets by fingerpicking. - Play only the tune.
No chord notes or anything like that - well not many of them at least. - Do whatever you want with the fifth string as long as you don't touch it while you're playing!
Generally there is very little useful you can do witht he fifth string: you don't want that high g or a ringing all the time, and nine times out of ten it's technically easier to do without.
If you want to go a step further:- Use the "Irish tenor banjo" right hand position witht the little finger anchored on the banjo head close to the bridge.
- Tune the first string up to an e.
The "Chicago" or "Guitar" tuning - DGBE seems to be much better suited for Irish solo playing than standard five-string banjo tuning DGBD / DF#AD (remember we leave the fifth string out). The tunes often reach up to a high a, and it's a great advantage to be able to reach that note without changing left hand position.