What is the function of 'le' in collocation with 'cabraigh'? On breis.focloir.com they say it introduces the indirect object, for instance Chabhraíonn sibh leim You helped me. And suddenly here we use leis in the same way as in english. How could we say then The girls are helping the man with the book? ''Cabhraíonn na cailíní leis an bhfear leis an leabhar and we have to figure out which object is direct and which one is indirect out of context?
The context is that cabhraigh le is a phrasal verb; one doesn’t “help somebody” in Irish, one “helps with somebody”. Thus, with Cabhraíonn na cailíní leis an bhfear leis an leabhar, the fear is a somebody and the leabhar isn’t, so that’s how the English translation “The girls help the man with the book” can be unambiguously determined; there’s no chance of translating it as “The girls help the book with the man” because cabhraigh le is only used in reference to living creatures (or, I suppose, with undead creatures in certain contexts).
Just out of curiosity, I frequently hear the phrase, "I was out with the girls the other day" or something similar, and they are referring to a group of women that are in their 70's. Does the Irish understand a particular age range for cailin/cailini, are there 70 year old cailini?
The root of the verb is the same as singular, imperative form. As far as I understand, it's the form used in most dictionaries. "Help the girls with the book" would be "Cabhraigh lena gcailíní leis an leabhar", unless you're talking to more than one person, when it would be cabhraígí....
Edited for accuracy (below)