'old_lm_arpa' is the arpa LM corresponding to the seed LM,
'old_lang_test_dir' lang_test directory of seed models,
'old_lm_arpa' is the arpa LM corresponding to the seed LM,
'ds_lm_dir' from previous step,
'int_ds_lm_dir' contains the interpolated dialog state specific LMs.
Note that interpolated dialog state specific LMs perform better than the dialog state specific LMs created by previous command. But the previous command is essential to obtain 'ds_lm_dir'.