deps: i18next 10 -> 23, react-i18next 7 -> 14

Modernizes the whole i18n stack:
- 48 translate([], {wait:true}) / translate() HOCs -> withTranslation()
- react.wait:true -> react.useSuspense:false
- whitelist -> supportedLngs; added compatibilityJSON: 'v3' so our
  natural-language keys + v3 _plural layout keep working (custom
  separators ss/eth/dj preserved)
- backends: xhr -> i18next-http-backend (client), sync-fs ->
  i18next-fs-backend (server); dropped i18next-localstorage-cache
  (was enabled:false); languagedetector 2 -> 8
- ReSendEmail: <Interpolate> (removed in v10) -> <Trans values={{email}}/>,
  dropped the removed bare t export
- saveMissing handler signature (lngs, ns, key, fallbackValue)

Silences the per-component Translate/I18n legacy-context warnings.
Browser-verified es/en switch and <Trans> interpolation on /fires;
REST smoke byte-identical.

imports/startup/client/i18n.js

@@ -3,9 +3,8 @@ import i18n from 'i18next';
 import { Meteor } from 'meteor/meteor';
 import { Tracker } from 'meteor/tracker';
 import { ReactiveVar } from 'meteor/reactive-var';
-import backend from 'i18next-xhr-backend';
+import backend from 'i18next-http-backend';
 import LngDetector from 'i18next-browser-languagedetector';
-import Cache from 'i18next-localstorage-cache';
 import { T9n } from 'meteor-accounts-t9n';
 import moment from 'moment';
 import 'moment/locale/es';
@@ -31,21 +30,9 @@ const detectorOptions = {
 
 export const i18nReady = new ReactiveVar(false);
 
-const cacheOptions = {
-  // turn on or off
-  enabled: false,
-  // prefix for stored languages
-  prefix: 'i18next_res_',
-  // expiration
-  expirationTime: 7 * 24 * 60 * 60 * 1000,
-  // language versions
-  versions: {}
-};
-
-i18nOpts.cache = cacheOptions;
 i18nOpts.detection = detectorOptions;
 i18nOpts.react = {
-  wait: true,
+  useSuspense: false, // was `wait: true` pre-react-i18next-10
   defaultTransParent: 'span'
   // https://react.i18next.com/components/i18next-instance.ht
   /* bindI18n: 'languageChanged loaded',
@@ -55,8 +42,10 @@ i18nOpts.react = {
 
 const sendMissing = true; // Meteor.isDevelopment;
 if (sendMissing && Meteor.isDevelopment) {
-  i18nOpts.sendMissing = true;
-  i18nOpts.missingKeyHandler = function miss(lng, ns, key, defaultValue) {
+  i18nOpts.saveMissing = true;
+  // Modern signature is (lngs, ns, key, fallbackValue, ...); key/fallback keep
+  // the same positions, so we still only need those two.
+  i18nOpts.missingKeyHandler = function miss(lngs, ns, key, defaultValue) {
     Meteor.call('utility.saveMissingI18n', key, defaultValue);
   };
 }
@@ -71,7 +60,6 @@ function setT9(lang) {
 
 i18n.use(backend)
   .use(LngDetector)
-  .use(Cache)
   .init(i18nOpts, (err, t) => {
     // initialized and ready to
     if (err) {