Vaci-sankhara is thought (vitakkavicārā vacīsaṅkhāro, SN 41.6; MN 44)
The easiest answer to the question is from MN 18:
yaṁ sañjānāti taṁ vitakketi
What you perceive, you think about.
AN 6.63 uses the term 'voharati', which I guess in its context here means 'definitions' or 'expressions' used in/as/facilitating 'communication' rather than 'verbal speech' used for communication.
Sujato in his translation has used the word 'communication', which in English can mean to transmit mutual understanding, such as:
to convey knowledge of or information about : make known
succeed in conveying one's ideas or in evoking understanding in others."a politician must have the ability to communicate"
(of two people) be able to share and understand each other's thoughts and feelings.
"we don't seem to be communicating—we need a break from each other"
convey or transmit (an emotion or feeling) in a non-verbal way. "the ability of good teachers to communicate their own enthusiasm"
For example, DN 9 unambiguously says:
From a cow comes milk, from milk comes curds, from curds come butter,
from butter comes ghee, and from ghee comes cream of ghee. And the
cream of ghee is said to be the best of these.
While it’s milk, it’s not referred to as curds, butter, ghee, or cream
of ghee. It’s only referred to as milk.
While it’s curd
or butter
or ghee
or cream of ghee, it’s not referred to as anything else, only under
its own name.
These are the world’s common usages (lokasamaññā), terms
(lokaniruttiyo), means of expression/definition/communication (lokavohārā) and descriptions
(lokapaññattiyo), which the Realized One uses to communicate
(voharati) without getting stuck on them.