A translation will vary in duration, especially if you have human editors reviewing it. Bigger messages will take longer, but a chat message should never take more than a few seconds to translate. Therefore, if you see the Translating... message for too long, something might have gone wrong.
The strongest possibility is that a bug affected the translation request. If this is the case, we advise you to repeat the translation request, so that you have the quickest possible resolution.
Should this fail to solve the issue, please report it issue to customer.happiness@unbabel.com or use our support form, identifying the message UID and/or conversation ID (label).