Yoshio Anderson is a Japanese interpreter.
During Lind L. Tailor's broadcast, Anderson interprets what Tailor says into Japanese. The language Tailor is speaking, that Anderson is interpreting from, is not stated. Since the broadcast is from Interpol, it is likely either English or French.
Anderson is never seen in the series, and is only mentioned the one time in chapter two.
In other mediaEdit
In the Death Note live-action film, Tailor's words are interpreted from English into Japanese, but the name of the interpreter is not stated.
In the Death Note television drama, Yoshio Anderson is actually an alias used by L when he interprets what Tailor says from English into Japanese for the broadcast. Additionally, once Tailor dies on live television, L speaks directly to Kira without a voice synthesizer, so it's obvious that it was him.