Modern equivalent for "arrah", or for its Irish version, "yarrah"

The term is present in most dictionaries which define arrah as an expression of excitement.

arrah [ ar-uh ]

Irish

Expressing excitement or strong emotion.

• ‘‘Arrah, don't be talking nonsense,’ Elmer exclaimed’

Etymology - Late 17th century from Irish ara, arú.

(Lexico.com)

arrah (interjection)

Irish —used to express surprise or excitement.

(M-W)

The daily edge website suggests the following usage:

“Ara“ - Ara is used to give an indication that you’re really not too fussed about something. It can also be used to start pretty much any sentence:

• Ara I might go. I might not.

“Ara Musha“ - When ara is used in conjunction with musha then it means something else entirely. It’s a term of endearment or affection:

• Ara musha you poor craythur, you’ll be grand.