As far as "safe" meaning that your messages cannot be hacked or other privacy concerns, I have not heard about violations of privacy. However, with that being said, there are a few other reasons that QQ chat would not be considered safe and reliable.
The international version of QQ chat is connected to a website which is full of viruses. In order to get around this serious virus risk, you will need to use a third party to run the QQ chat. This prevents the viruses from getting into your computer and instead the third party can filter them out using their own anti-virus software.