I felt I had to share this as I use Vicipéid everyday. The Irish language Wikipedia has helped me learn a lot of Irish (e.g. countries, place names, grammar etc.) and editing it I feel helped the language to grow.
The link to Vicipéid (Irish Wikipedia) is: https://ga.wikipedia.org/wiki/Pr%C3%ADomhleathanach
Wikipedia is a great place for any language! I'd recommend first trying to read articles on subjects you're vaguely familiar with (or quickly read about them on Simple English wiki before proceeding) so you can deduct the meaning of new words from context rather than checking the dictionary all the time. :)