Sumerian is the first language for which there is written evidence and its literature is the earliest known.
Mark Saltveit has compiled a collection of Sumerian proverbs. Here are a few to get you started:
- Flies enter an open mouth.
- A dog entered a tavern and said: "I can't see a thing. I'll open this one!"
- I am a lady who wears large garments. Let me cut my loincloth!
- For his pleasure he got married. On his thinking it over he got divorced.
The Electronic Text Corpus of Sumerian Literature (ETCSL) comprises a selection of nearly 400 literary compositions recorded on sources which come from ancient Mesopotamia (modern Iraq) and date to the late third and early second millennia BCE.
Thanks to Bruce who pointed me in this direction.