There are many people who do not have google on their phones. Those with who understand how serious of a privacy and security violation that is. Will go to great lengths to free themselves from this evil.

Relying on Google translate isn't a viable option for a FOSS project like #Amethyst. Which, correct me if I am wrong, goes to great lengths to preserve security and privacy for their users. Using anything of their products on a project like Amethyst is like saying I am wearing protection during sex. 

However you still get an STD (privacy and security violation) from a hooker (google services), because the protection you are wearing is a bullet proof vest and not a condom (trustworthy FOSS). If you use the google play version and have google services on your phone with other proprietary apps that violate your rights. No matter what Amethyst does to try and protect you. If there is still google anything involved, your privacy and security are an illusion. They don't really exist. 

Those who feel this way and have freed themselves from google slavery. Do not have a native translation feature on the FDroid version.  So having either a baked in auto translation feature that works natively offline on android, or via a Linux server running a tor language translation service to Amethyst only users. 
Would be the best long term solution that retains the spirit of #Amethyst.