Latin

The ancient language of the Romans, which Sheldon studied at school until 5th grade. Both, Sheldon and Howard know the Latin names of insect species.

Howard: The common field cricket, AKA Gryllus assimilis, which is Latin for "suck it, you lose".

Sheldon: The snowy tree cricket. AKA, Oecanthus fultoni. Which is Latin for "I'll suck nothing". Of course I'm joking because the Latin for that is nihil exsorbibo.

Note: This dialogue from The Jiminy Conjecture also implies that Sheldon either remembers particular Latin quotes or that he is able to translate short phrases into Latin. This would be a rather remarkable skill considering that Latin today is only an official spoken language in the Vatican-City state [1].

Sheldon has also used Latin phrases before, such as "Post hoc, ergo propter hoc" for flawed reasoning (0301), "Reductio ad absurdum" for illogical arguments (0107) and "Ipso facto" for direct consequences (0403).