0. place install_thrax.sh into $KALDI/tools/extras/

1. recompile openfst with necessary option "--enable-grm" to support thrax:
* cd $KALDI_ROOT/tools
* make clean
* edit $KALDI_ROOT/tools/Makefile, append "--enable-grm" option to OPENFST_CONFIGURE:
OPENFST_CONFIGURE ?= --enable-static --enable-shared --enable-far --enable-ngram-fsts --enable-lookahead-fsts --with-pic --enable-grm
* make -j 10

2. install thrax
cd $KALDI_ROOT/tools
sh extras/install_thrax.sh

3. add thrax binary path into $KALDI_ROOT/tools/env.sh:
export PATH=/path/to/your/kaldi_root/tools/thrax-1.2.9/src/bin:${PATH}

usage:
before you run anything related to thrax, use:
. $KALDI_ROOT/tools/env.sh
to enable binary finding, like what we always do in kaldi.

sample usage:
sh run_en.sh
sh run_cn.sh