Have a second plane shift prepared in case you arrive somewhere inhospitable enough that you need to leave immediately. Also, pre-cast life bubble - since that's 3 5th level spells counting the initial plane shift you may need to make & use a scroll or similar.
If no one in the party speaks Terran then you'll need tongues or elemental speech prepared in all probability.
Stone shape might be handy.
Although having terran language is an extremely useful. This is because, as a cleric, you have summoning spells.
This mostly comes up due to the fact that you could easily use low level summoning spells for scouting. While wind elementals are great for flight and speed (and thus general coverage), earth elementals can earthglide, making them great scouts. Combine that with tremor sense, and they might get through a lot without being noticed
Admittedly, if there were burrowers and tremor sense users, this would be the place. But even then... it is an earth elemental- they belong there. At most, enemies might try to attack it thinking it is a vermin. They don't suspect that they are summoned minions like they would on the mortal plane.
So having at least a single summon monster II prepared is hardly a bad idea, as well as having that skill point in linguistics.
Get a Necklace of Adaptation, too, as a backup. It'd be a bummer to have a dispel or greater dispel take out your source of breathable air.
Did I say "a bummer"? I meant "fatal".