One community at that time where there was likely to be a lot of translating was among religious dissidents. Following the Albigensian Crusade, many Cathars relabelled themselves as Bogomils and ended up in the Balkans. And when the Byzantines crushed the Bogomils, they converted to deviant or crypto-Gnostic forms of Islam, as Pomaks in Bulgaria or Bektashis in Albania and Bosnia. And the Bektashis had already merged with mystical forms of Shiism in Turkey, creating the Alevi religion in Anatolia and the (not really Islamic at all) Yarsani (aka Ahl-e-Haq) group in Iraq and Iran. And the Bektashi/Ahl-e-Haq in turn were a late manifestation of central Asian shamanism given an Islamic veil. So in the late Middle Ages, you had a fairly solid chain of two-way influences running beneath the radar all the way from France to Mongolia, but with no common language.