I’m a talker: I’ll have a conversation with anybody. But as a professional French-English interpreter working in the criminal justice system, I can be a different person’s voice every day. I’ve translated for murderers and suspected terrorists.

I remember my first job in a crown court. I was twenty-seven, in the dock with a drug smuggler who had been paid to carry cocaine in her suitcase from South America. She was about my age, with a child. I could feel my heart pounding before I opened my mouth. She was found guilty and sent to prison. Every case I’m involved in hangs on the accuracy of what I say; when someone’s life or freedom is on the line, I feel additional pressure.

I translate verbatim and in the first person. To add or omit anything would distort the dialogue. I have to find the right words and register, but I’m also required to mirror emotion and intonation. Silences are important, too; they are all part of how we converse. The way words are delivered changes a whole message. You feel a bit like an actor at times. I once spoke for a doctor accused of manslaughter who was so desperate to prove his innocence. For that day, I felt that I became him.

Cultural nuances can be crucial. We understand ‘mon frère’ to mean ‘my brother’. In African cultures it can be ‘my friend’, too. Whether a brother or friend arranged to get someone out of prison can change a whole asylum case.

It’s not just about being bilingual;  I work with different lexicons. Communicating court terminologies is different to speaking for an asylum seeker in counselling, or a child in speech therapy, where a professional relies on my exact delivery to form a proper opinion.

I did a French degree followed by a Masters in translation and a diploma in public service interpreting, which trains you to speak in police, local government, health or legal settings. One day, I can be interpreting at a Premier League football club, translating for a footballer receiving a drugs ban; the next, I might be sitting in a high-security prison.

The criminal stuff is really my bag; a world that’s not my own. I love being a fly on the wall. I spent two days in a police control room listening in to a wiretap in a high-profile unsolved murder case. In reality, there was a lot of him turning on his TV and flushing the toilet, but it felt like a civic duty.

The conversations I am part of are confidential and often traumatic. I have repeated explicit sexual assault details, spoken for a teenage girl who had been trafficked into prostitution, and translated for a torture victim — but I can’t discuss any of it with a friend on the way home. I have to deal with them in my head, which can be hard.

Everyone has their limits. I find the health stuff hardest, particularly where children are involved. I had to tell one lady that she had cancer. It was the only time I’ve cried in a job. But these conversations are a privilege, too. I have acted as a birthing partner for women who are otherwise alone. One lady, an asylum seeker, asked me for baby names during labour. I had watched Peter Pan that weekend; she called her daughter Wendy.

I’m not the doctor, the police officer or the judge in these rooms; I’m just somebody who did a French degree and loves languages. I feel honoured to be part of those dialogues. These conversations couldn’t take place without me.

• As told to Deborah Linton