Add backup-related error messages and improve UI styles

- Updated English, Spanish, Russian, Simplified Chinese, and Traditional Chinese locale files to include new error messages related to backup and restore processes.
- Added prefix and suffix strings for the "cached empty" message to enhance clarity in user prompts.
- Enhanced the management CSS with new styles for the backup browser refresh prompt to improve layout and user experience.

webapp/src/components/BackupCenterPage.tsx

@@ -193,7 +193,7 @@ export default function BackupCenterPage(props: BackupCenterPageProps) {
   const [downloadingRemotePercent, setDownloadingRemotePercent] = useState<number | null>(null);
   const [restoringRemotePath, setRestoringRemotePath] = useState('');
   const [deletingRemotePath, setDeletingRemotePath] = useState('');
-  const [localError, setLocalError] = useState('');
+  const [, setLocalError] = useState('');
   const [restoreProgress, setRestoreProgress] = useState<BackupProgressState | null>(null);
   const [restoreElapsedSeconds, setRestoreElapsedSeconds] = useState(0);
   const [confirmLocalRestoreOpen, setConfirmLocalRestoreOpen] = useState(false);
@@ -974,7 +974,6 @@ export default function BackupCenterPage(props: BackupCenterPageProps) {
         }}
       />
 
-      {localError ? <div className="local-error">{localError}</div> : null}
       {restoreProgress && typeof document !== 'undefined' ? createPortal((
         <div className="restore-progress-overlay" aria-live="polite">
           <section className="restore-progress-card restore-progress-modal">

webapp/src/components/backup-center/RemoteBackupBrowser.tsx

@@ -32,6 +32,18 @@ export function RemoteBackupBrowser(props: RemoteBackupBrowserProps) {
       : t('txt_downloading_percent', { percent: props.downloadingRemotePercent });
   };
 
+  const renderRefreshPrompt = () => (
+    <div className="backup-browser-empty">
+      <span className="backup-browser-refresh-prompt">
+        <span>{t('txt_backup_remote_cached_empty_prefix')}</span>
+        <button type="button" className="btn btn-secondary small" disabled={!props.canBrowse || props.loadingRemoteBrowser || props.disableWhileBusy} onClick={props.onRefresh}>
+          {t('txt_backup_remote_refresh')}
+        </button>
+        <span>{t('txt_backup_remote_cached_empty_suffix')}</span>
+      </span>
+    </div>
+  );
+
   return (
     <>
       <div className="backup-divider" />
@@ -42,8 +54,10 @@ export function RemoteBackupBrowser(props: RemoteBackupBrowserProps) {
 
       {!props.destinationIsSaved ? (
         <div className="backup-browser-empty">{t('txt_backup_remote_save_first')}</div>
+      ) : props.loadingRemoteBrowser && !props.remoteBrowser ? (
+        <div className="backup-browser-empty">{t('txt_backup_remote_loading')}</div>
       ) : !props.remoteBrowser ? (
-        <div className="backup-browser-empty">{t('txt_backup_remote_cached_empty')}</div>
+        renderRefreshPrompt()
       ) : (
         <>
           <div className="backup-browser-path">