i18n: Add and Imporve translation

[fengkx]

Previously #67

2024 Hacktoberfest update

There are some words updated in zh-cn.yaml, zh-tw.yaml and en.yaml but no other languages.

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The bot supports switching language using /lang command. For now, It supports languages listed in README.

We can add more translation by adding a yaml file named by a lower case language code in the i18n directory. For example: https://github.com/fengkx/NodeRSSBot/pull/52

The translation should be based on zh-cn.yaml or en.yaml which is maintained by repository owner(get updates with latest strings) PR welcome.