US plaintiffs must serve Mexicans via Mexico-court

*Lawsuit involves Grupo Televisa but may have wider impact

*Ruling centers on decade-old translation error

By Gina Keating

LOS ANGELES, April 16 (Reuters) - U.S. lawsuits against Mexicans must be served through Mexico's designated central authority, a federal judge in Los Angeles has ruled in a case involving broadcaster Grupo Televisa (TLVACPO.MX) and others.

The decision could have a big impact on litigation in which U.S. plaintiffs sue Mexican entities, an attorney in the case said on Thursday.

Also, the commonly accepted practice of serving lawsuits in Mexico by mail or by official process server is improper and was condoned only by a decade-old translation error in Mexico's Hague Convention declarations, U.S. District Judge John Walter found in a ruling filed on Wednesday.

The case is a copyright infringement and breach of contract lawsuit by music publisher OGM Inc against Mexican broadcaster Grupo Televisa (TLVACPO.MX), U.S. Spanish-language TV network Univision and related entities.

Televisa attorney Seong Kim, of Steptoe & Johnson in Los Angeles, said the case could have a "huge impact" on U.S. litigation against Mexican defendants.

"A lot of times, you serve someone in Mexico and there is no response and a judgment will issue," he said. "Now a defendant can come in and say, 'That judgment is nullified because the case wasn't properly served.'"