You switch from English to German. You open a project. All your standard walls and slabs turn yellow (missing library parts). Cause: The Archicad standard library is language-specific. Library_27_EN is different from Library_27_DE . Solution: You must load the new language’s library. Go to File > Libraries > Add Library... and navigate to the Archicad installation folder to manually load the Library_27_DE.lcf file. Use Library Migration Manager to map missing objects.