Here is a list of common error codes (and their interpretations and explanations), which Google Translate can return:

• 503 Service Unavailable response: If you are getting this error, it is most likely that Google has banned your external IP address and/or requires you to solve a CAPTCHA. This is not a bug in this package. Google has become stricter, and it seems like they keep lowering the number of allowed requests per IP per a certain amount of time. Try sending less requests to stay under the radar, or change your IP frequently. Please note that once an IP is banned, even if it’s only temporary, the ban can last from a few minutes to more than 12-24 hours, as each case is different.
• 429 Too Many Requests response: This error is basically the same as explained above.
• 413 Request Entity Too Large response: This error means that your input string is too long. Google only allows a maximum of 5000 characters to be translated at once. If you want to translate a longer text, you can split it to shorter parts, and translate them one-by-one.
• 403 Forbidden response: This is not an issue with this package. Google Translate itself has some problems when it comes to translating some characters and HTML entities.