I don't believe arm is slang, but it does have various meanings. It could be your arm on your body, like you said, and as an adjective, it means poor or lame, as in that was a lame excuse.
Black bear in German is der schwarze Bär
because we say things differently but still mean the same thing
Because there is no such thing!
Yes, but U-boat is confined to German subs. the word is literally Unterseeboot- Undersea Boat, which is what a submarine is.
"Pee" is slang for urinate; "peeing" is slang for "urinating".
Slang for thing
No such thing, or it's slang.
Try "snore"
Buggar all is a curse. It means the same thing as d*mn it all or f*ck it all.
Slang term for women's breasts.
Well, there's no such thing as a baby anchor, so it must be slang!
The two words mean the same thing. Colloquialism is the fancy term for slang.