My computer had no speaker connected for the past week due to some hardware change. Usually ran over HDMI and used the TV as speaker, but had to replace my Graphicscards with another one that doesn't support HDMI. Currently my TV is connected via DVI - HDMI adapter. My prefered sounddevice was set to the standard speaker, but I also deactivated, reactivated and used different devices in my list when trying to fix the problem.

I had subtitles ON with the expectation to see positions of enemies, but it didn't show anything. I made a backup of my options and deleted the old file to reset any settings. My brother on the other hand had full visuals of subtitles, but with working sound it wasn't exactly necessary.

I connected very cheap speaker to my Audio output and with ingame sound working the subtitles also work.

This is a very strange bug for a system that was designed for people that don't have sound or have a disability and might not even need speaker in general.