Honestly the term 'a lot' is very difficult to say, in the period (the 14th-17th centuries) that I am most familiar with lay literacy was increasing but in old Medieval Europe true literacy meant knowing latin and your vernacular tongue. This put, by Brady in his German Histories, literacy at a paltry 2% in the era before the printing press. The nobility would have indeed had access in time and resources to pursue literacy and latin if they were so inclined but most didn't to a high degree.

French was a much more likely language of communication across Europe, especially as local dialects could be so wide ranging as to be mutually unintelligible. Scribner (oral culture), Pettegree (sections of his reformation world on printing), and Davis are good places to follow up. However, you give such a wide time period that you may want to specify more.

For example, the Hungarian parliament, until the creation of the dual monarchy, was held wholly in Latin as a way of mediating between the linguistic soup of that part of the empire without giving undue prominence to non-German groups.

The time period you are reffering to is too wide to give a specific response to your question... Even in the 11th century noblemen from different 'countries' would not use latin over, let's say, vernacular languages to engage in a conversation.

Please narrow your time period... But one thing you have to keep in mind is that : Yes, the study of latin was common in noble families (even before/after your time period). Yes, most pieces of archive (administrative ones like lend lease for instance) are written in medieval latin up until the late 15th century in France. No, latin would not be practical to communicate, even during an earlier time period (6th to the 8th century) as vernicular latin/lingua romana was already spread in Europe and quite different from latin itself.

One example that comes to mind right now and that may shed a light on this question are the Oaths of Strasbourg made in 842. The oaths were made in vernaculars (Old French and Theodiscus/Tuduesque or Old German). A written version in Latin does exist though. However latin was not used during the oath per se in front of the armies assembled that day.

At work atm, will developp this awswer later on