Senan can elaborate more, Lily, but I suspect at least some of the Irish boarding at Queenstown would have been familiar with Shakespeare - but through the original English rather than through a Gaelic translation.
The Gaelic language had declined in use up until the Gaelic Revival movement of the late 19th/early 20th Century - a movement that really gained momentum with the formation of the Gaelic League in 1893. Gaelic language revival was at the core of Irish cultural nationalism, and had a key role in Irish nationalism itself. I imagine - and Sen can correct me here - that given that background, an English playwright would be an unlikely choice for a Gaelic translation at that particular time.
Well, it's helpful that one of the characters in the novel can speak both English and Gaelic, so she very well could've encountered Shakespeare in English. I'm not sure if Shakespeare's work was translated into French, though... Thank you, Inger!
There were bound Gilded Age collections of sonnets, and of the plays, sometimes grouped as the Comedies, the Tragedies, etc. Yes, there were also French translations in text and performed on the French stage. The great Sarah Bernhardt (Rosine Bernard)made a lasting impression as Cordelia in KIng Lear (Le Roi Lear)back in 1867, and took the title role of Hamlet herself in 1899.
There were translations existing of Shakespeare as early as 1604, and by 1912, some plays, especially Romeo and Juliet, Hamlet, Julius Caesar and Othello, existed in translations in German, (the first non-English translation of Romeo and Juliet), Portuguese (1607), Dutch, French (1645), Russian (1748), Italian (1756), Polish (1788),Hungarian (1797),Spanish (1798),Romanian (1848),Greek (1856),Serbian (1860),Icelandic (1878)Czech (1883) and Finnish (1879). As yet, I can't find any Gaelic translations of Shakespeare by 1912. Senan- got a free moment?!