Language introduced by Ludwig Boltzmann (4)
I believe the answer is:
igbo
'language' is the definition.
(I have seen 'Nigerian language ' mean 'igbo' so perhaps 'language' could also mean 'igbo')
'introduced by ludwig boltzmann' is the wordplay.
'introduced by' indicates the answer is hidden within the clue.
'IGBO' is hidden within 'ludwig boltzmann'.
(Other definitions for igbo that I've seen before include "language in Nigeria" , "Nigerian language" , "people abroad" .)