tavla -tav-ta'a- gismu

x1 talks/speaks to x2 about subject x3 in language x4.

Not limited to vocal speech, but this is implied by the x4 without context of some other medium of conversation (use cusku, casnu, skicu, ciksi for weaker implication of vocal communication); converse/discuss/chat (= simta'a, simsku, vricysimta'a for a conversation not clearly delimited by subject). See also bacru, cusku for actual expression, casnu, darlu, skicu, ciksi, bangu.

In notes:

bacru
x1 utters verbally/says/phonates/speaks [vocally makes sound] x2.
bangu
x1 is a/the language/dialect used by x2 to express/communicate x3 (si'o/du'u, not quote).
casnu
x1(s) (mass normally, but 1 individual/jo'u possible) discuss(es)/talk(s) about topic/subject x2.
ciksi
x1 (person) explains x2 (event/state/property) to x3 with explanation x4 (du'u).
cusku
x1 (agent) expresses/says x2 (sedu'u/text/lu'e concept) for audience x3 via expressive medium x4.
darlu
x1 argues for stand x2 against stand x3; [an opponent is not necessary].
skicu
x1 tells about/describes x2 (object/event/state) to audience x3 with description x4 (property).
ba'usku
s1=b1 (agent) says s2=b2 (sedu'u/text/lu'e concept) for audience s3 through expressive medium s4.
ba'usle
s1 (phone/speech sounds) is a segment of utterance/speech stream s2=b2.
ctununta'a
x1=n1=c5 is a lecture / an event of verbal teaching by x2=t1=c1 to audience x3=t2=c2 about subject x4=t3=c4 in language x5=t4 with facts taught x6=c3.
da'arta'a
t1=d1 quarrels with t2=d2 about issue t3=d3 in language t4.
filta'a
t1=f2 speaks fluently to t2 about subject t3 in language t4 under conditions f3.
lujrinsku
x1=c1 (person) justifies/expresses justification x2=k2 for x3=p1's complicated-ness in aspect x4=p2 to audience x5=c3 via expressive medium x6=c4.
nalta'acni
c1=t1 is withdrawn, feeling emotion c2 about c3=t3 from t2.
nunflapai
n1 is a trial of dispute j2 involving people f3.
sagjvetavdraci
d1=s2=t3 is a musical/operetta about d2 composed/written by d3 for audience d4=s3=t2 with actors d5=s1=t1.
samta'a
t1 talks via computer to t2 about t3 in language t4.
sezyta'a
x1 talks to himself/herself/themselves about x2 in language x3
ta'arsi'u
s1 (set) discuss subject t2 in language t4.
ta'avru
x1 is talking noise / background chatter to x2 observed via senses x3 of x4 talking to x5 about x6 in language x7.
terlisri
l3 tells/narrates about subject l2 with narration l1 to audience l4.
verfavzu'i
x1 is a developmental disability that hinders/disrupts x2's ability to do x3
vokta'a
x1 speaks (vocally) to x2 about x3 in language x4
vozyvozylisri
Storyteller x1=l3 tells audience x2=l4 story/tale/yarn/narrative x3=l1 about plot/subject/moral x4=l2.
goi'e (exp!)
assign sentence or tu'e...tu'u group to sumti
jborefota
x1 is a pair of Lojbanists who frequently talk to each other in Lojban by telephone.
lenguua
x1 is a language used by x2 to express x3 (du'u, not quote)
mlauca
x1 mentions or alludes to x2 while talking to x3
skaipe
x1 contacts x2 by video-telephone/video-chat/teleconference service (product) x3 provided by (company/producer/provider) x4