LibreTranslate is a free and open source machine translation API, which was released in 2020, with Raspberry Pi compatible ARM64 images dropping in December 2022. The project is entirely self-hosted, with its translation engine powered by the open source Argos Translate library, rather than Google or Azure.
If you run LibreTranslate on your Raspberry Pi, you can either access translations through dedicated FOSS apps, or through a web front-end accessible with any browser.
How to Install LibreTranslate on Your Raspberry Pi
LibreTranslate won’t run on just any Raspberry Pi as it requires a fair bit of processing power, and images are only available for ARM64, rather than earlier 32 bit versions. So make sure that you have a Raspberry Pi 4B running a recent 64-bit OS.