Speak so as to be Understood

1 Cor 14 : 4 "He that speaketh in an [unknown] tongue edifieth himself; but he that prophesieth edifieth the church."

So if I go to church and speak a language that only I understand, it benefits only myself and nobody else. Selfish?

I think if there is no interpreter it is better to remain silent when addressing to the congregation. If there is no interpretation then it benefits just the one whose language is uncommon to the hearers, but it does not mean that person is selfish, it is only a lack of interpretation.