in back_translate.sh:
sbash ${SCRIPTS_ROOT}/prepare_de_monolingual.sh
the bash files are not in ${SCRIPTS_ROOT}, but in src.
also in back_translate.sh:
#binary
for shard in $(seq -f "%2g" 0 ${shards_num});do
the loops in bash are inclusive so if shards_num is 3 meaning (0,1,2) the loop will try to get shard 3 which doesn't exist so I replaced it with
#binary
for shard in $(seq -f "%2g" 0 $((shards_num - 1)));do