If one is not satisfied with any of the meanings of 'sovacassataa' (or
any other word for that matter) found in translations and
dictionaries, one can always turn to studying how the word is derived
and explained according to the commentaries and native grammars.
This word presents some difficulties but after doing a bit of digging,
I've come up with a rough translation of "the nature of the activity
of pleasant speech". I will explain how I came up with this. On p. 52
of the Atthasaalinii, there is some valuable information on the
derivation and meaning of 'dovacassataa' and following that is a
remark on 'sovacassataa' saying that it is just the opposite of
'dovacassataa'. On the basis of the latter term we can start with
'suvaco' (= sukha.m vaco -- pleasant speech) to which the taddhita
affix 'ya' (.nya) in the sense of 'tassa kamma.m' (the activity,
action, occupation thereof) is added which causes the 'u' of 'su' to
change to 'o' giving us 'sovacassa'. I think the double 's' can be
explained with reference to Sanskrit 'vacas', thus: vacas + ya -->
'vacassa' by assimilation. Finally, a second taddhita affix 'taa' in
the sense of 'tassa bhaavo' (the nature, state, quality thereof, etc.)
is then added giving us 'sovacassataa'. A good explanation of both
taddhita affixes can be found in sutta 490 of Ledi Sayadaw's
Niruttidiipanii (available on the CSCD disk). There you will also find
some helpfu details on the usage of the term 'bhaava' which covers
quite a bit more than the term 'kamma' (= kriyaa). I think 'the nature
of the activity of ' is probably not right. I certainly need to get a
better handle on the usage of affixes like 'taa' in the several senses
of 'bhaava' (jaati, dabba, gu.na, kriyaa, naama).