The mod adds new sounds for walking on certain block materials, and while these point to subtitle translation strings, there are no translations actually associated with them. This causes the strings themselves to appear in the captions:

Either actual subtitles should be added to the lang files so these display correctly, or these sounds should just be repointed to use the generic vanilla footsteps subtitle text.

commenting on this thread to say i have the same problem, and that i had to remove the mod because of this since minecraft has no native way to resize subtitle text

Duplicate of #141