Never concatenate several human-readable strings. You can use something like:
```javascript
          var error_msg = _('ssidCannotBeEmpty');
```

where, in `settings.en-US.properties`, you could have this if you want to factorize `ssid-name`:
```ini
ssidCannotBeEmpty={{ ssid-name }} cannot be empty.
```

But I’d probably use a simple string instead:
```ini
ssidCannotBeEmpty=The SSID name cannot be empty.
```