According to the message sent by Rick Dietrich, Secretary and Deputy Commissioner, Workers' Compensation Appeals Board:

The Appeals Board held with regard to interpreter services liens that: 1) pursuant to the employer's obligation under Labor Code section 4600 to provide medical treatment reasonably required to cure or relieve the injured worker from the effects of his or her injury, the employer is required to provide reasonably required interpreter services during medical treatment appointments for an injured worker who is unable to speak, understand, or communicate in English; and 2)  to recover its charges for interpreter services, the interpreter lien claimant has the burden of proving, among other things, that the services it provided were reasonably required, that the services were actually provided, that the interpreter was qualified to provide the services, and that the fees charged were reasonable.

The Appeals Board also stated: "In reaching our holding on an interpreter lien claimant's burden of proof, we emphasize that the discussion which follows is not all-inclusive and that, in any given case, the lien claimant also might be required to carry its burden with respect to issues we have not addressed, including but not limited to the issue of injury arising out of and in the course of employment, if contested.  The methods [to carry its burden] we discuss are neither exclusive nor mandatory."

Read the en banc decision at http://www.dir.ca.gov/wcab/EnBancdecisions2011/GuitronJose.pdf