Sect. 51of the German Copyright Law (UrhG), applies to everything that is protected by copyright, i.e. also to technical rules published outside Germany. If standards are to be cited beyond this scope, this requires permission. For this purpose, a more detailed description of the scope and purpose of the planned citations should be provided to DIN's Legal Department.
Please fill the form out at https://www.din.de/en/about-standards/standards-and-the-law/reproduction-new and send it to DIN.