Should it be 'bhí pian ina theanga aige' ?
Indeed it should.
GRMMA. Shíl mé chomh maith. Is é pian i mo thoin uaireanta.
Tuigim.
Or, slightly different word order? ie "Bhí pian aige ina theanga" similar to these examples from th'Internet "Bhí pian aige ina ghiall" and "... agus pian aige ina sciathán clé".
Yes, that would be another possibility.