“بِ” (bi)means “in / with / by.” It is a preposition: it links this word to the next word or phrase.Corpus grammarP — prefixed preposition.
“لِسَانٍ” (lisānin)means “In language” in this verse. It is a noun. a naming word. Here it is masculine, not specific, genitive.Corpus grammarN — genitive indefinite noun.