In Angular 6, now that I think I comprehend how to make the i18n files and utilize them (e.g. https://angular.io/guide/i18n), I am wondering about maintenance of said files. If
You can use ngx-i18nsupport. It uses xliffmerge to merge translation files automatically after running ng xi18n.
xliffmerge
ng xi18n
I ended up making a solution for myself until something better comes along: https://github.com/maplion/angular6-i18n-helpers
So far, it is working pretty well for me.