Basque language

Basque is a language isolate ancestral to the Basque people, who are indigenous to and mainly inhabit the Basque Country, a region spanning an area in north-eastern Spain and south-western France.

Sourced

 * Cést un langage estrange que le Basque... On dit qu’ils s’entendent, je n’en croy rien.
 * Translation: Basque is really a strange language... It is said that they understand one another, but I don't believe any of it.
 * Joseph Justus Scaliger, talking in 1604–1606.