They are redundant, as far as I can tell.
Posted under Tags
So, empty_textbubbles is for when ALL speech bubbles are blank? The different terminology and format ("blank" vs "empty", "speech" vs "text" and underscore vs no underscore) suggests that the tags were created independently by different people but refer to the same thing. Furthermore, empty_textbubbles should imply blank_speech_bubble in this case but it doesn't, currently. Whether we keep both tags or not, I think some improvements can be made.
Edit: Or do you mean that "speech bubble" is a subset of "text bubble", because the later also includes thought bubbles etc? I think this difference is not very important and doesn't really justify an extra tag. Also, using singular for one tag and plural for the other is confusing in this case.
My vote goes to unifying both to a new tag called "blank_text_bubble" which is for all images that contain one or more text bubbles of any sort that are blank.
Updated by CaesarsSalad
Seems someone emptied the empty_textbubbles tag... Given that blank speech bubble implicates speech bubble I hope they didn't unilaterally decide to move them over. Then again with empty word bubble being aliased for some reason to blank speech bubble, even though you also get thought bubbles and styles of text bubble that are used for neither speech nor thoughts, this situation does seem to be a bit of a mess.