Judo began in Japan and uses Japanese terms. In Japanese, you indicate someone that does something with the suffix 'ka.' So you would be called a judo-ka.
Yes its called Judo flip by Asheru
The red competitor is called "hong" (홍) The blue competitor is called "chung" (청)
dojo
In japan, mat is Tatami and we just call it Judo Tatami.
Judo is the martial art referred to as the "gentle way."
'Shido' is the term for a penalty
Opponent
I assume you are talking about boxing, judo or wrestling. Those are the colour competitors have to wear. They draw for a colour and each competitor has uniforms in each colour.
Judo training uniform is called Judogi or you can just called Gi.
He/She is called competitor or participant.
It is called the Dojo it means place of the way
Judo is japanese, so it remains judo in all languages.