THAMES Valley Police has spent £5.6m on translators and interpreters for suspected criminals in the last five years.
Last year it spent £1.16m, the sixth consecutive year the bill topped £1m.
The money is spent on face-to-face interpreters, telephone interpreting and translation of documents when dealing with suspects, accused and witnesses.
Anyone contacting the police who can’t speak English will also get a paid translator.
Simon Reed, vice chairman of the Police Federation, said the costs were “unreasonable” and had a huge impact on forces.
He said: “It is something that has to be done but it is unfair to expect police to bear all the costs.”
Experts have warned that segregating immigrant groups could lessen the need to speak English.
The most recent census data for Oxford showed that a third of people – 44,239 – currently living in Oxford were born abroad.
The Thames Valley Police and Crime Commissioner Anthony Stansfeld, who oversees police spending in Oxfordshire, declined to comment when approached.