Dear Jacques,

> But I wonder if the Sanskrit that the Buddha spoke, if
> he did, must not have been closer to a still very
> "Vedic" dialect (Ardha Magadhi?) rather than classical
> Sanskrit as Panini who definitely stabilized Sanskrit
> is posterior to the Buddha by about 2 centuries.

Sanskrit didn't exist at the time of Buddha. In the suttas the
Brahmanical language is referred to as 'chandaso'. Panini also used this
term. The meaning of it - "metrics, prosody" indicates that this
language was then used mostly for the purposes of reciting Vedas.

The language Buddha spoke, which now became Pali, is indeed very similar
to Ardha-Magadhi preserved in Jain canon. You can check it yourself at
the webpages:

http://www.jainworld.com/scriptures/samansuttam9.asp

Yours with Metta,

Dmytro