Hi Bernd
The positioning of certificate text can be controlled to a limited extent through see https://totara.help/docs/customise-certificates for details . It is difficult to precisely align the text with the images and fixed text due to different fonts , character size and language so requires tweaking as the preview is not always accurate.
From memory a way around this is to create a graphic of all the fixed text and images with space for the content that changes and save this in the border image folder (the border also includes region outside the border) This allows precise positions of fixed text and graphics.
regards