@sampo2910 of None is the only option that works, then that's probably the only one your email provider supports. It should be fine as long as you don't need your emails to be perfectly secure.
All of our translation efforts are handled on Transifex (https://www.transifex.com/nodebb/nodebb/), but in general, yes... fixes and incorrect translations would be handled there, and custom changes specific to your community you'd make to those files directly.