“Ecumenical” refers to the work for unity among different denominations of Christians. The question you raise is an inter-religious one because it relates to members of other world religions rather than other members of other Christian churches. The dialogue among Christians is not an interfaith or interreligious dialogue because, even though we belong to different traditions of Christian faith, we are still all members of the one world religion known as Christianity.
Regarding our relations with members of other religions such as Buddhism and Judaism, the Second Vatican Council’s A Declaration on the Relationship of the Church to Non-Christian Religions (Nostra Aetate), recognizes the existence of “truth and holiness” in other religions, and encourages Catholics to engage “in dialogue and collaboration with followers of other religions, carried out with prudence and love.” It also clearly affirms the imperative to “recognize, preserve and promote the good things, spiritual and moral, as well as the socio-cultural values found among” peoples of other religious traditions.
There are aspects of Buddhism and Judaism that can help you as a Catholic practice your faith even better. For example, a central practice in Judaism that is also found within the Christian tradition but not faithfully practiced is keeping the Sabbath Day just for praying and playing, for rest and relationship. Seeing how seriously religious Jews take their Sabbath practice (for Jews, Saturday, but for Christians – Sunday, the day of the Lord’s resurrection) can challenge you to strengthen it in your own spiritual life.
And an example in Buddhism might be its emphasis on living with mindfulness (being attentive to the present moment) or the prevalence in Buddhism of the practice of meditation. When you encounter beneficial practices like these in other religions, it sends you back to your own treasure chest to dig more deeply in it in order to find what your Christian faith offers along these lines. And you can find that it offers a lot. For example, Centering Prayer (which you can find more about at www.contemplativeoutreach.org), or Christian Meditation (again found at www.wccm.org ), or you might find the book The Sacrament of the Present Moment by Jean-Pierre de Caussade, a little classic of Christian spirituality.
What’s to be avoided is a smorgasbord approach, i.e. a little something from this religion and that religion without going deep into any religion. In order to strike oil, you have to go deep. Shallow wells won’t do it. The interreligious encounter requires us to really be rooted in our own faith, and to celebrate and benefit from what we find of God in other faiths. I’ve heard the Dalai Lama say on a couple of occasions when he was speaking to large crowds and knew there were lots of Christians out there: “We don’t want you to become Buddhists. We simply want you to take what you find of value in Buddhism and work with it to help make you a better Christian.”