zh-CN: translate src/basic-syntax/variables.md, src/basic-syntax/type…

[Eventide]

…-inference.md and some words in SUMMARY.md (#796)

• zh-CN: translate src/basic-syntax/variables.md, src/basic-syntax/type-inference.md and some words in SUMMARY.md

• Use "类型推导" for "Type Inference"

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