When a translator completes or advances a translation they will create a pull request, that must be reviewed by another peer. A Pull Request or PR is a method of submitting proposed changes to the code base.
Translators would post a link to their pull request in the chat room of the language; asking for reviews. If you see a message requesting review of a translation, visit the pull request and find the tab
"Files changed" right under the PR’s title. There you will be able to see the changes in the translation in two columns, to the left you will see the original file and to the right the changes proposed.
If you want to suggest an improvement to the translation in one line (a.k.a inline commenting), click on the
+ (plus sign) that appears next to the line number when you move the cursor over, in the dialog that pops up you can write your suggestion.