The problem is being blamed on a Ministry of Justice-backed interpreter service which police sources say is failing to provide interpreters fast enough.
The scheme was supposed to save West Midlands Police £750,000 every year.
But it has forced officers to release some arrested foreign suspects on bail because they cannot get interpreters.
In one case, it took West Midlands Police two weeks to find an interpreter for someone who volunteered to make a statement in an Asian language.
In some instances, the force has had to bring in more expensive interpreters from Leeds and Manchester.
The force signed up to an agency of interpreters backed by the Ministry of Justice in November to reduce its annual bill of nearly £2million.
The company, Applied Language Solutions, said it had boosted its resources in the past two weeks and "implemented significant improvements" to deal with problems. But police chiefs have admitted that, in a small number of cases, foreign suspects arrested for low-level crimes such as shoplifting have had to be freed on bail before questioning.
One source said a number of former police interpreters will not assist the force again, claiming they were treated poorly. "The company are recruiting some more people but it has not been what was hoped," the source said.
One Birmingham interpreter, who did not sign up with ALS because of a drop in pay and conditions, has revealed how she was called at 7.45am on the very first day of the new contract as possible cover.
Marie Adamova, a 46-year-old Czech interpreter, said: "There has been a boycott as these problems are also happening at the Ministry of Justice."
A police spokesman said in all cases where the suspect had been released on police bail they had returned to the station to answer questions at a later date.
"We acknowledge that there are a number of operational service issues and we are working hard with ALS to address these," he said. He added that "public safety has not been compromised".
An ALS spokesman said: "We have implemented a number of significant improvements and increased our resources considerably in the last two weeks, in order to improve performance."