(Quite) A bit late in responding, but the way Cesare "pronounced" it, it seemed to be in Italian:

The word "seguro" is romanized as セグーロ in Japanese.
They are technically in Pisa after all, even though Cesare's speaking to a fellow Spaniard. In
Cesare, Spanish tends to get spelled out, not romanized (as in the example above):

So, assuming that their representation method is consistent (it could be that they tend to speak in longer phrases when using Spanish and that's why they've used this method), it seems Cesare did speak in Italian.