I guess you are using the 0.6 branch.
KenLM ist used to generate the words.arpa and lm.binary and you use the Deepspeech native client to generate the trie file. And you will use the lm.binary and trie for training.
If -o 3 is returns an error, use 2. It is to find common word combinations and the more the better, but you want to get going
And don’t build the native client, download it: