Type your translation next to each English line. Where a word is highlighted, fill in the local word you want highlighted. If the highlight has two words, press Enter to put the second one on a new line, as it will look in the video. When you are done, download your two files and send them back.
Choose the English video from your computer to see your subtitles on top of it. The video stays on your computer and is not uploaded anywhere. Click a time on the left to jump to that line.
The video is cropped to a square from the centre, like the 1:1 version. The big word in the middle is a rough simulation of how a highlight could look: the real size and font come from the video editor. If your word is too wide for the frame, you will see a warning.