"Tá sé i gceist agam an leabhar sin a léamh" can be translated as "I plan to read that book" or "I plan on reading that book", though I would say that the intention is somewhat weaker, it doesn't refer to a definite plan, but something you're just thinking about doing. As a dictionary entry it might be "rud a bheith i gceist agat a dhéanamh".