Noor Mohammad, 30, from Bradford, was impersonated by an unqualified Pakistani national on the run from the authorities who had outstayed his student visa.
Mian Ahmed Jan, 27, visited headquarters at Greater Manchester Police (GMP) six times as he signed off exhibits which could have been used in future court proceedings.
Manchester Crown Court was told that Mohammad agreed for his friend to attend appointments in his place but was unaware he would go on to pose as him by using a fake ID card and forging his signature.
Sentencing him to four months in jail, suspended for 12 months, Judge David Stockdale QC told him: "The work which interpreters carry out for the police and the courts and for other agencies is serious and important work.
"The public places its trust in interpreters and you breached that trust. This is a serious breach of trust. A clear message must go out that breach of trust placed in registered interpreters will be dealt with severely by the courts."
Timothy Brennand, prosecuting, said Pashtun speaker Mohammad was approached by GMP in February 2009 to assess cassettes seized in house searches. He agreed to help but sent Mr Jan, also from Bradford, in his place when he realised he could not attend because he was away on holiday.
When later interviewed by police, he said he did not tell them of the switch because self-employed interpreters regularly fill in for each other and claimed: "It happens all the time, its all right." He did not know that Mr Jan was not a qualified interpreter.
The man, who he had known for a couple of months, had entered Britain in September 2005 on a student visa but was not granted an extension when it expired.
He had told Mohammad that he had undertaken translation work for counter-terror officers in London. He was supposed to leave the country by February 13, 2009, but only departed two months later.
The fraud came to light by chance when the defendant's travel expenses were queried by the interpreter liaison officer.
Ricky Holland, mitigating, said there was no financial benefit to his client who received cheques in his name totalling 931.97 but did not cash any of them.
He was a well-educated man with no previous convictions who is now unemployed because of his "considerable loss of grace".
There were no complaints about the standards of Mr Jan's work and it did not appear to have caused a security breach.
Mohammad, of Croft Leigh Court, pleaded guilty at an earlier hearing to fraud. He was also ordered to perform 100 hours of unpaid work.