The two new mobs do not have their sound subtitles like when they are hurt, killed, etc., with subtitles on.
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This also isn't the first time a new mob is added w/o the subtitles for it. There have been others in the past.
Duplicate of MC-91893 (all of the missing subtitles for various sounds are collected there)
It also affected the other 2 snapshot versions with the turtle and phantom.