Hi @Robot_Lover, it is possible to play text/audio files out to the speaker from ROS software. There is a ROS tutorial on the subject available at this link. In summary, a ROS package called “sound_play” has everything needed to go from a string to audio played out on the speaker. On Stretch, everything comes pre-installed (just ensure that the right device is selected in speaker settings, as shown by Aaron in this post). You may simply run the following two commands in separate terminals:
$ roslaunch sound_play soundplay_node.launch
[in a separate terminal]
$ rosrun sound_play say.py "hello robot"