Other translations of this song are by
1) Lady Gregory (a contempory of Yeats) - "Donall Oge", published in Brendan Kennelly, ed, "Between Innocence and Peace: Favourite Poems of Ireland", Cork: Mercier (no date given, but recent publication)
2) Seán Lucy - "Donal Ogue", published in Lucy, Unfinished Sequence", Dublin: Wolfstone, 1979 nad Seán Dunne, ed., "Poets of Munster", London: Anvil and Dingle, Co. Kerry: Brandon , 1985

Both have the verse about milking the cow; here is Lady Gregory's version:

O Donall Oge, it is I would be better for you
Than a high, proud, spendthrift lady:
I would milk the cow, I would bring help to you;
And if you were hard pressed, I would stike a blow for you.

In the chapter of Munster versions in the book, I found this Irish for the above verse::

A Dhomhnall Óig, b'fhearr dhuit mise agat
Ná bean uasal uaibhreach iomarcach
Do chrúdhfainn bó agus do-ghéanainn cuigean duit,
Is, dá mba cruaidh é, do bhuailinn buille leat.

Here is the "If you come at all, come when stars are peeping" verse in Irish, from one of the Munster versions published in

Má thagann tú 'n aon chor tar ist oidhche [ist =ins an t; oidhche=oíche]
Tar sa dorus go mbeidh an tsíon ann
Fiar(fh)óghaidh mo mháithrín cia ro díobh thú,
A's dearfad-sa leithe gur ab síol don gaoith thu.

(Munster is the southern-most province of Ireland.)