Bluff, Bluff, Bluff to the Right and Left

[Jungian]

He could bluff a Druid into believing he is a fellow Druid, but not by speaking Druidic. It's a secret language know only by Druids, so without being one there is conceivable way of the beguiler knowing the language. I don't think Druids instantly began speaking Druidic when they encounter another druid, I always imagined it being only spoken during the most sacred of rituals. Druids also have a high wisdom score, so his lies would need to be well crafted.

He is a beguiler using any of his image spells can make for a perfectly suited performance.