feat: add fallback locales to ensure we display something

This will help reduce the problem for niche players that sometimes
get overlooked by the majority when adding content.

addon/-private/decorators/localized-attr.js

@@ -1,3 +1,5 @@
+import { getOwner } from '@ember/application';
+import { isEmpty } from '@ember/utils';
 import { attr } from "@ember-data/model";
 
 export default function (...args) {
@@ -11,7 +13,25 @@ export default function (...args) {
   attrComputed.get = function () {
     const value = getter.call(this);
 
-    return value && value[this.getFieldLocale()];
+    if (!value) {
+      return;
+    }
+
+    const {
+      localizedModel: { allowAnyFallback = false, fallbacks = [] } = {}
+    } = getOwner(this).resolveRegistration('config:environment');
+
+    if(value[this.getFieldLocale()] || (!allowAnyFallback && !fallbacks.length)){
+      return value[this.getFieldLocale()];
+    }
+
+    let key = fallbacks.find(key => !isEmpty(value[key]));
+
+    if (!key && allowAnyFallback) {
+      key = Object.keys(value).find(key => !isEmpty(value[key]));
+    }
+
+    return value[key]
   };
 
   attrComputed.set = function (value) {

config/environment.js

@@ -1,5 +1,14 @@
 'use strict';
 
 module.exports = function(/* environment, appConfig */) {
-  return { };
+  return {
+    localizedModel: {
+      // If this is true the decorator will get the value in any language
+      // if neither the preferred language nor the fallbacks yield anything.
+      allowAnyFallback: false,
+      // Set fallback languages in order they should be tried
+      // if the preferred language has no value.
+      fallbacks: [],
+    },
+  };
 };