rusty

If your German is rusty, it's like the bike you left out in the rain too many times that turned brown and flakey on the metal parts. Like your bike, your German skills became rusty, meaning they're suffering from neglect.

You can also describe yourself as rusty: you used to do flips on your skateboard, but you haven't practiced in a while and now you're a little rusty. Rusty can also refer to the color of rust, which is a reddish-brown — a rusty-colored dog, for instance. Anything made of iron or steel that you leave outside in the elements is likely to oxidize and become rusty, covered with rust.

Definitions of rusty
1

adj covered with or consisting of rust

“a rusty machine”
rusty deposits”
Synonyms:
rusted
having accumulated rust

adj of the brown color of rust

Synonyms:
rust, rust-brown
chromatic
being or having or characterized by hue

adj impaired in skill by neglect

Synonyms:
out of practice
unskilled
not having or showing or requiring special skill or proficiency

adj ancient

Synonyms:
hoary
old
of long duration; not new