In the empty segments (those for which the application doesn't suggest a translation), a dotted line appears in the left margin of the empty segment. At the same time a message appears in the top of the window. This message disappears once the translation is achieved and saved.
those red dots appear bacause a QA check has been run in the past by someone who took care of a job for this document before for instance. That is why since there were no translations entered for those segments errors have been detected and the message 'Translation is missing' appears on top of the interface.
Once you enter translation red dots will disappear.