Morning. As the suggestions I did page 14 of this thread have been nicely welcomed, please let me add another one :


You should target police departments of big cities.

i.e the same day, Paris police will have to deal with : Chinese tourist victim of pickpocket, illegal immigrant from Africa and a thief from eastern europe. In today's society, I think Police departments are one of the biggest regular consumer of translation services. However, they will only work with mandated and official interprets.
You should recognize such interprets in your app (they will need to send copy of ID + copy of the document allowing them to translate for the police), and they get this special status.

Once you estimate to have enough officials interprets (or maybe hire few of them for the marketing campagne duration), offer a trial to police departments of some big cities.
You just send them a Raspberry Pi, with your app already installed and some tokens in it. They will be able to test your project for free, and as simple as possible.

This can be a big pool of clients, having unlimited and daily needs for interprets services.
Huge potential in my opinion