A language expert is commonly referred to as a linguist. Linguists study the structure and usage of language, including grammar, syntax, semantics, and phonetics.
A person who is an expert in grammar is called a linguist or a grammatician.
A linguist is a person who is an expert in language or languages, including the structure, meaning, and use of languages. They often study the historical development of languages and their significance in different cultures.
They are called "linguistic or language communities."
A person who does sign language is called a "sign language interpreter" or a "signer."
Expert, Knowledgeable, etc..
linguist
pullicologist
A language expert is commonly referred to as a linguist. Linguists study the structure and usage of language, including grammar, syntax, semantics, and phonetics.
a semanticist
An expert at table talk is called a deipnosophist.
Horologist
A mathematician.
Horologist
Horologist
A toxicologist is an expert in poisons and their effects on living organisms.
The experience of the expert, the educational background of the expert, and the ability of the expert to talk in clear, concise language. There may be more, but this is all I know.