For example, some torts have names that aren't used in other contexts in English and appear to have come in from French for their legal usage's purpose. But what is the origin of the name of trover for that civil wrong, and what causes a judge in a common law case through the ages to decide that instead of simply ruling on an issue before him at hand, he is going to define and name and in a certain sense completely canonise a more general and fundamental concept?
This is a purely linguistic question, despite the hope to discover a special legal process. Somebody uses a word or phrase in order to communicate an specific idea. Somebody else thinks "That's a good way to put it" and uses the same or very similar expression to convey that idea. Enough people do this and it becomes "conventional". The word itself is not made up, it already existed, and was simply applied in a specialized way (e.g. "tort" is an ordinary French word meaning "wrong, mistake" taken into English in a more specialized manner).
If you want to know the history of a legal term, you have to read relevant historical rulings to see when the word was first used. That is how we know that current technical term "consideration" derives, from around the time of Henry VIII, that it derives from rulings referring to "assumpsits" which were made "in consideration of" an obligation. "Trover" is a sufficiently old term in law that you will have a hard time pinning down first use and the pattern of expansion.
what is the origin of the name of trover..?
Common-law action to recover the value of personal property that has been wrongfully disposed of by another person.
Late 16th century from an Anglo-Norman French noun use of Old French trover ‘to find’.
A lot of legal terms are of French origin due to that being the principal language used by the Crown and nobility following the arrival of William the Conqueror in 1066. And before that, the Romans and Vikings also put their stamp on the lexicon.