Ok, I think I found the perfect solution, In the readme I added near open-source "(almost)" with a link to the libraries and models section when I explained clearer what components are open-source, closed-source, and cc-by-nc.
it's the closest, but it's a very broad and not so well known term, maybe defining my app open source is not technically a perfect term, but it's the clearest in describing it (considering that in the libraries and models section I specified which are open-source and which are not, Ml-Kit, used to recognize the language, for example is closed source), if a developer doesn't see the open source writing anywhere he will only get confused in understanding what the license of my app is. However, based on your feedback I added the specification (in the "libraries and models" section) that NLLB has a non-commercial license.
Instead of "almost", maybe "Open Source Code (and free for non-commercial use due to model licencing)" since your contributions are free as in freedom,and that is amazing!
Thank you for building this, I have been using a web interface connected to a local server for inference but the latency was about 1 second, too much for my taste!
I think it is too long for the preface, but I will better specify that my code is open source in the libraries and models section, thank you for the suggestion and the appreciation!