RAW: Sounds like it wouldn't matter. They are affected by the Geas, they take the damage.
RAI: Reading the spell more carefully, note that if a creature "does not understand" the spellcaster (know their language), the spell has no effect. This sounds like the target needs to KNOW that they are disobeying the caster. Their very disobedience is what triggers the spell - reinforced by the fact that this is psychic damage, not any other type of damage. I think the intent is, if there is no way to understand that you're disobeying the caster, then the spell does not trigger until the caster somehow again makes them aware of their wishes in regards to original commands.
RAF: That's a heck of a way to open a campaign, that every time you try to do a certain thing, you get a near-fatal brain aneurysm and have to be saved from death's door by others in the party. Better for campaigns that are starting near 5th level or so, such that it wont kill someone outright.