You are using a trial subscription of the Translate add-on, which has a lower monthly limit than the actual paid subscription.
You have reached that limit. While on the trial, you can still use the add-on with daily free quota. If you would like to raise the limit, you can purchase the actual paid membership, which has a higher quota limit than the trial version.
The paid quota should be enough for most users. If you exceed it too, please contact me. You have to understand that I am paying Google based on the number of characters used. I am gathering usage statistics to see how I can improve the add-on and make the quota high enough to satisfy as many users as possible not causing financial losses for me at the same time.