refactor: use lang keys, fix typo

public/language/en-GB/admin/admin.json

@@ -4,7 +4,7 @@
 
 	"acp-title": "%1 | NodeBB Admin Control Panel",
 	"settings-header-contents": "Contents",
-	"changes-saved": "Changed Saved",
+	"changes-saved": "Changes Saved",
 	"changes-saved-message": "Your changes to the NodeBB configuration have been saved.",
 	"changes-not-saved": "Changes Not Saved",
 	"changes-not-saved-message": "NodeBB encountered a problem saving your changes. (%1)"

public/src/modules/settings.js

@@ -555,13 +555,14 @@ define('settings', ['hooks', 'alerts'], function (hooks, alerts) {
 						callback(err);
 					} else if (err) {
 						alerts.alert({
-							title: 'Error while saving settings',
+							title: '[[admin/admin:changes-not-saved]]',
+							message: `[[admin/admin:changes-not-saved-message, ${err.message}]]`,
 							type: 'error',
 							timeout: 2500,
 						});
 					} else {
 						alerts.alert({
-							title: 'Settings Saved',
+							title: '[[admin/admin:changes-saved]]',
 							type: 'success',
 							timeout: 2500,
 						});