There is only one language within the world of Memento Mundi. You will never meet someone who speaks a foreign language. There are however, numerous different ways of writing this language down, such that the phrase “languages” is a term which relates exclusively to the written word.
The glossary below contains some musings on language from an IC perspective.
One of the most fascinating endevours a scholar of communication can partake in is to visit a culture isolated from the sea and talk to people about their understanding of nautical terminology. For example, I once visited Junnes and spoke to the locals about their understanding of the term “Boat”, a term nearly synonymous with “Sled” in the local dialect as a device for traversing the desert. Wanting to investigate further, a few years later I managed to convince a Junnes local to visit me in Acryn. Taking her to the Port she agreed that what we were looking at were clearly “Water Boats”. When I asked her why they weren't “Water Sleds” she simply said that they didn't sit high enough in the water.
A source of frustration for many scholars of the magical arts is the persistence of apparently meaningless terms in the public consciousness, chief among these being “Necromancy” and “Necromantic Energy”. These are terms which anyone versed in the magical arts understands to be meaningless, and yet the terms persist in a way which seems at odds with every other witnessed communicative phenomenon.
Scholars who have investigated what constitutes “Necromantic Energy” (in an attempt to uncover some basis for the persistance of this term) have found the exact boundaries of what constitutes Necromancy are somewhat fuzzy, but the basis appears to be that something has to have died as part of a ritual in order for that ritual to be Necromantic. Some Scholars suggest this demonstrates a folk belief of a living being's vital essence being a suitable source of magical power (a belief which has been firmly established to be false).
Unfortunately to this day the reason why these words exist eludes us.
The Soul, an important word for us all, it describes an essential nature of humans which is different for creatures. Many assign some sort of persistence of the Soul beyond the life of its mortal container. Unfortunately, and despite much research into the subject, no evidence for a persistant Soul has been found. Of course it is trivial to demonstrate that something leaves the body upon death, but the exact nature of this continues to defy explanation.
The term dragon is to an extent well defined. Any culture with a basic understanding of magic ties the term to 5 great entities which in some way produce, give, or govern magic. Even cultures which do not have this basic magical understanding still associate the term with extremely powerful beings, and where a specific number is given it is always five.
However, there are also some rather surprising differences. In the area surrounding the city of Acryn the images depicting the dragons are of great and mighty lizards, scholars suggest this probably stems from the presence of extremely large predatory lizards in the area up till a few hundred years ago. Around Margush the term conjures different imagery, that of giant elemental humanoids. The people of Junnes depicted them as colossal many-limbed sea-creatures more akin to the term Leviathan in sea-going cultures (although the people of Junnes portrait them as being desert-dwellers). What limited evidence we have from the Serradic empire indicates that they are portrayed as 5 young men & women, the only culture known in which the motifs of primal behaviour and giant size are missing.
We have very little evidence for change (or lack there-of) in the meaning of words over time. One of the few pieces of evidence we do have is from magisters who have chosen to name their spells with names incongruent with their function. The names of these spells inevitably fall out of use, being lost to all but the most pedantic of magical history. An example many will be familiar of is the Scribing spell which transmutes a page into a bolt of lightning: “Namtar's Boot”.