The bulk of this site is in German (there are one or two English articles) but the editor is a big advocate of open source and hobby electronics and has written it for all ages so if German is not your first language it is still fairly easy to follow.
Literally hundreds of articles here, covering many diverse areas of electronics (basic analogue stuff, microcontrollers (Arduino, RPI and others), radio circuits and useful hints and tips. There are also links to sources for components that can be harder to find (and these suppliers do also have English sections on their sites).
