I've replied the following to the reporter:

• If the translation takes too much time, you might see an execution timeout message by Google; Google places a 6-min limit to the Google Apps Script execution, which is the underlying script behind SheetsL (Source: https://developers.google.com/apps-script/guides/services/quotas#current_limitations ). Please consider breaking down the translation into multiple executions. For example, if you are trying to translate 1000 cells at once and you are seeing the execution timeout message, you might want to try translating 500 cells at a time.
• If you are seeing the "Cell content length exceeds Google's limits" message, you should try to shorten or break up the contents of the cell in question.
• A screenshot of the error message that you are seeing might be helpful.

I will keep this thread updated.