Internationalize backup cost string

Author: trevor-signal

_locales/en/messages.json

@@ -7088,6 +7088,10 @@
     "messageformat": "Your subscription was not found. Renew to continue using Signal Secure Backups.",
     "description": "Description when a backup subscription used to exist but is not active"
   },
+  "icu:Preferences--backup-subscription-monthly-cost": {
+    "messageformat": "{cost} / month",
+    "description": "Text displaying the cost per month of the backup plan. Cost is an internationalized string, e.g. '$2.99' or '2,99 €'"
+  },
   "icu:Preferences--backup-messages-plan__description": {
     "messageformat": "Text + {mediaDayCount, plural, one {# day} other {# days}} media backup",
     "description": "Description of a backup plan that backups all of their messages (text) and recent ~45 days of media"

ts/components/PreferencesBackups.tsx

@@ -325,12 +325,13 @@ function getSubscriptionDetails({
       <>
         {subscriptionStatus.cost ? (
           <div className="Preferences--backups-summary__subscription-price">
-            {new Intl.NumberFormat(locale, {
-              style: 'currency',
-              currency: subscriptionStatus.cost.currencyCode,
-              currencyDisplay: 'narrowSymbol',
-            }).format(subscriptionStatus.cost.amount)}{' '}
-            / month
+            {i18n('icu:Preferences--backup-subscription-monthly-cost', {
+              cost: new Intl.NumberFormat(locale, {
+                style: 'currency',
+                currency: subscriptionStatus.cost.currencyCode,
+                currencyDisplay: 'narrowSymbol',
+              }).format(subscriptionStatus.cost.amount),
+            })}
           </div>
         ) : null}
         {subscriptionStatus.renewalTimestamp ? (