We have recently started using translate5 as a tool for reviewing translations. This tool was developed in Germany and can be used in a browser without the need to install any software. It is a fantastic solution for cases in which a client's in-house experts wish to review a translation. Reviewers can add comments or make changes to the translation, and the translator can then view these and respond with comments of their own if necessary. At the end of the review process, the final version of the translated document containing all amendments can be generated. Most importantly of all, all of these changes are added into the translation memory, meaning future translations will be even better!
You can find more detailed information about translate5 here: https://www.translate5.net/