$ sudo apt install libttspico-utils
$ pico2wave 
Mandatory option: --wave=filename.wav

Usage: pico2wave <words>
  -w, --wave=filename.wav     Write output to this WAV file (extension SHOULD be .wav)
  -l, --lang=lang             Language (default: "en-US")

Help options:
  -?, --help                  Show this help message
      --usage                 Display brief usage message
$ WAVE="`mktemp`.wav" && pico2wave -w $WAVE 'hello' && aplay $WAVE ; rm $WAVE

日本語には未対応

$ pico2wave -l ja-JP  -w /tmp/hoge.wav hoge
Unknown language: ja-JP
Valid languages:
en-US
en-GB
de-DE
es-ES
fr-FR
it-IT

Usage: pico2wave <words>
  -w, --wave=filename.wav     Write output to this WAV file (extension SHOULD be .wav)
  -l, --lang=lang             Language (default: "en-US")

Help options:
  -?, --help                  Show this help message
      --usage                 Display brief usage message

無理やり日本語

 WAVE="`mktemp`.wav" && pico2wave -w $WAVE "`echo "こんにちは" | mecab -Oyomi | uconv -x latin`" && aplay $WAVE ; rm $WAVE