runbau lujvo

r1=b1 is an artificial/constructed language used by b2 to express/communicate b3 (si'o/du'u, not quote).

Artificial languages do not necessarily have speakers, cf. bangu.

In notes:

pa'arbau
b1 is Esperanto.
rarbau
b1 is a natural language spoken by community b2 to express b3.