cer·ti·fi·ca·tion ( sûrˌtə-fĭ-kāˈshən ) noun - a. The act of certifying. b. The state of being certified. A certified statement.
Often when a client requests certification, what they are asking for is a signed and notarized statement that the translation is true, accurate, and correct "to the best of my knowledge and ability".
Certification and notarization involve an extra charge to cover the time and trouble for the service, the notary’s fee, and shipment of the certified paper copy.
There are agencies, such as the American Translators Association (ATA), that provide an accreditation to translators, (which some may refer to as certification), but this accreditation is not an all-encompassing test for advanced-level or in-depth translating. This job must be fully assumed by the translation agency, which puts the necessary time and effort into finding the most qualified people for the job.