M/C lives in US, I think in the SE. Translates either sound or inscriptions and meets another race living underground. Not Fantasy Lover's Perchance to Dream or Baen dead tree novel about stealing gems from underground race published about 10-15 years ago. 90% sure was on this site.
I think it my be epigraphy by zaliterr.
https://storiesonline.net/a/zaliterr
https://storiesonline.net/s/69304/epigraphy
I do not know if the story I am thinking of is the one you are looking for and honestly, I can not remember the title, but if it sounds close it might help searching for it. In the story I am thinking of the MC had just been released from jail and found out that a relative had passed and left everything to him. He found a society of (I think) elf like beings living below his relatives house. They only came out after dark and only for short periods due to pollution and other changes. Like I said I do not know if it is the one but it was a good story and might help in you search.
thank you. that is the one I was thinking of. I do not know if it will help the original poster but a darn good story. I may have to go back and re-read it.
