Speaking in tounges or Glossolalia happens (and has for many many years as BD pointed out) in many religions.   However, it is most common in some of the older Pagan or Shamanistic based faiths.  Occurrences of it generally happen in those faiths where the practitioner is seeking to be possessed by some type of "spirit" or other.

In Pentecostalism people are seeking to be possessed by the "Holy Ghost" and tongues is viewed as the evidence of that.   The common denominator of the occurrences is "spirit possession".    Now is to if the possession is real,  fabricated by the sub-conscious, or faked all together is probably another discussion.