The Oaths of Strasbourg provide a fascinating, Rosetta-stone like glimpse into the state of ninth century French and German, alongside what was then considered formal Latin as distinct from the emerging Romance languages.
But I’ve never heard of anything similar for Spanish, Italian, or Portuguese, to say nothing of Romanian or Sardinian.
Do historical linguists even have any examples of these languages from the same time as the Strasbourg documents? Are they on the Internet anywhere?