ca'irbau lujvo

x1 is the official language/standard language used by x2 to communicate x3.

See also catni, bangu.

In notes:

ca'irjugbau
x1 is the Standard Chinese/Standard Mandarin language used by x2 to communicate x3.
ca'irlipybau
x1 is the (standard) Filipino language used by x2 to communicate x3.