Which one sounds more natural in japanese...
日本はうつくしOr日本がうつくしい When describing someone would you use wa or ga?たなかのかみわみじかいOr たなかはかみがみじかい

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All of what you wrote in Japanese are a correct and natural way. 
It just about interactive problems.
日本はうつくしい→ it a like general truth.  Japan is the beautiful country.
but if you say 日本がうつくしい, the sentence must have specific detail about what do you think or feel beautiful about Japan.
ex. アニメは日本がいちばん。in English → Japanese Animation is the top of the world.

「たなかはかみがみじかい」means that  Mr. Tanaka is a man who has short hair 
but「たなかのかみはみじかい」refers to the specific point or truth which is Mr. Tanaka's hair is short.

Answer

日本がうつくしいたなかのかみがみじかい

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