i18n: Rename translations.js to i18n.js.

The file populates `windows.i18n`, so now
the file name matches our convention.

Note that the module really just initializes
`i18next` and then does this:

    window.i18n = i18next;

It doesn't really add any functionality to
third party library.

frontend_tests/node_tests/i18n.js

@@ -13,10 +13,10 @@ set_global('page_params', {
 
 // All of our other tests stub out i18n activity;
 // here we do a quick sanity check on the engine itself.
-// We use `translations.js` to initialize `i18next` and
+// We use `i18n.js` to initialize `i18next` and
 // to set `i18n` to `i18next` on the global namespace
 // for `templates.js`.
-zrequire('translations');
+zrequire('i18n');
 
 run_test('t_tag', () => {
     const args = {

static/js/bundles/app.js

@@ -18,7 +18,7 @@ import "flatpickr/dist/plugins/confirmDate/confirmDate.js";
 import "sortablejs/Sortable.js";
 
 // Import App JS
-import "../translations.js";
+import "../i18n.js";
 import "../feature_flags.js";
 import "../loading.js";
 import "../schema.js";

static/js/bundles/portico.js

@@ -1,4 +1,4 @@
 import "./common.js";
-import "../translations.js";
+import "../i18n.js";
 import "../portico/header.js";
 import "../../styles/portico/portico-styles.scss";