The voice files for Mirmulnir's five specific lines are just generic dragon roars in the English version. They still appear as lines if you have subtitles open, and they also are voiced lines in other language versions.
I asked USKP user Nextmastermind, who has worked with the Interesting NPCs mod, to voice the lines. For your consideration, here they are. I have renamed the WAVs with their assigned names, lipped them, FUZed them, then set up their directory.
A note: Translators will need to unpack the USKP BSA to remove these and then repack since many already have working Mirmulnir combat taunts and death crys. This probably has to be done with all dialog fixes anyway...