"The lady has food."
Translation:Tá bia ag an mbantiarna.
Mantiarna: no "caol le caol agus leathan le leathan"?
Is "ia" a diphtong here too? How can one tell when a group of two vowels is a diphtong?
Yes, ia is a diphthong. Ia and ua are always diphthongs; ei and oi are diphthongs only before syllable-final ll. Two vowels followed by bh, dh, gh, or mh in a stressed syllable can also form diphthongs, e.g. leabhar, leigheas.