Fix code tests for #8276 for real this time

Add utilFetchJson to get around some quirks of d3.json and use it for coreFileFetcher
Load real general English locale strings at the beginning of code tests

modules/core/file_fetcher.js

@@ -1,4 +1,4 @@
-import { json as d3_json } from 'd3-fetch';
+import { utilFetchJson } from '../util/util';
 
 let _mainFileFetcher = coreFileFetcher(); // singleton
 
@@ -54,7 +54,7 @@ export function coreFileFetcher() {
 
     let prom = _inflight[url];
     if (!prom) {
-      _inflight[url] = prom = d3_json(url)
+      _inflight[url] = prom = utilFetchJson(url)
         .then(result => {
           delete _inflight[url];
           if (!result) {

modules/util/index.js

@@ -26,6 +26,7 @@ export { utilEntitySelector } from './util';
 export { utilEntityOrMemberSelector } from './util';
 export { utilEntityOrDeepMemberSelector } from './util';
 export { utilFastMouse } from './util';
+export { utilFetchJson } from './util';
 export { utilFunctor } from './util';
 export { utilGetAllNodes } from './util';
 export { utilGetSetValue } from './get_set_value';

modules/util/util.js

@@ -572,3 +572,14 @@ export function utilUnicodeCharsCount(str) {
 export function utilUnicodeCharsTruncated(str, limit) {
     return Array.from(str).slice(0, limit).join('');
 }
+
+// Variation of d3.json (https://github.com/d3/d3-fetch/blob/master/src/json.js)
+export function utilFetchJson(resourse, init) {
+    return fetch(resourse, init)
+        .then((response) => {
+            // fetch in PhantomJS tests may return ok=false and status=0 even if it's okay
+            if ((!response.ok && response.status !== 0) || !response.json) throw new Error(response.status + ' ' + response.statusText);
+            if (response.status === 204 || response.status === 205) return;
+            return response.json();
+        });
+}