They're called Mansfield bars in the US, named after the actress Jane Mansfield who died after colliding with a trailer. They're not required federally and not particularly effective as they're generally not inspected or maintained.
There's probably an "official" name in some dusty Ministry of Transport document like "side protection collision bar" or some such, and TÜV probably calls it something like "Seitenaufprallschutzgerätüberlaufschutzausrüstung" or some damn thing.
Hinterer Unterfahrschutz
https://www.trucknews.com/features/are-standards-for-trailer...
https://www.iihs.org/news/detail/iihs-recognizes-semitrailer...