A 7-year-old girl said she had been raped and repeatedly molested over the course of a year. Police in Montgomery County, Md., acting on information from a relative, soon arrested a Liberian immigrant. They marshaled witnesses and DNA evidence to prepare for trial.

What was missing — for much of the nearly three years that followed — was an interpreter fluent in the suspect's native language. A judge recently dropped the charges, not because she found that Mahamu Kanneh had been wrongly accused, but because repeated delays in the case had, in her view, violated his right to a speedy trial.

"This is one of the most difficult decisions I've had to make in a long time," Katherine Savage said from the bench Tuesday, noting that she was mindful of "the gravity of this case and the community's concern about offenses of this type."

Loretta E. Knight, the Circuit Court clerk responsible for finding interpreters, said her office searched exhaustively for a speaker of Vai, a tribal language spoken in West Africa. They contacted the Liberian Embassy, she said, and courts in all but three states. Linguists estimate that 100,000 people speak Vai, mostly in Liberia and Sierra Leone.

In arguing to save the case, Assistant State's Attorney Maura Lynch said that dismissing the indictment "after all the efforts the state has made to accommodate the defendant would be fundamentally unfair."

Prosecutors, who cannot refile the charges against Kanneh, are considering whether to appeal Savage's ruling. Kanneh was granted asylum in the United States, according to State's Attorney John McCarthy. A conviction could have led to deportation proceedings.

Kanneh's attorney, Theresa Chernosky, declined to comment.

The proliferation of languages resulting from immigration trends is presenting courts with a novel challenge, legal and linguistics experts say. Rarely, however, does a court have such difficulty finding an interpreter that a criminal case must be dropped.