In this case I (en-gb native) initially thought extravert was some tertiary alternative to extrovert and introvert; then assumed it was errant/en-us spelling.
I'd think of extro- and intro- as looking out and in respectively. Extra- and intra- would be externally additive and internally additive; like a connection outside a defined group and inside such a group respectively.
tl;dr this was an edge case for me.
