However, language model adaptation is a more straight-forward problem compared to translation model adaptation, because various measures such as perplexity of adapted language models can be easily computed on data in the target domain.
language model adaptation has been well studied in various work (Clarkson and Robinson, 1997;Seymore and Rosenfeld, 1997;Bacchiani and Roark, 2003;Eck et al., 2004) both for speech recognition and for machine translation.