Perhaps this is related to the thread. Perhaps it is not.
"Informant"
noun
1.
a person who informs or gives information; informer
2.
a person who supplies social or cultural data in answer to the questions of an investigator.
3.
Linguistics. a native speaker of a language who supplies utterances and forms for one analyzing or learning the language.
Synonyms
1. source, adviser, tipster.