In most cases it is easy to reset the keyboard.
setxkbmap de
in a terminal window will do it for you.
This kind of setting will not survive a reboot, but probably the action that caused the change of keyboard was also only temporary.
-o-
Afterwards, you can reboot the computer and check what keyboard you get.
If not correct after reboot you should click the icon with a cog wheel and a wrench, and look into the settings for language and keyboard.
Please try to remember, what programs you were running when or just before this happened - running some application programs or maybe installing or updating some program package (updating can be automatic, but should not change the keyboard).
-o-
Maybe the keyboard was changed to English (US English is the default). It matches the description, but also some other languages could match that description.