i18n: Add and Imporve translation

[fengkx]

2020 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.

[dubaid]

Added pt-br - https://github.com/fengkx/NodeRSSBot/pull/68

[fengkx]

es-es.yaml Spanish translation is missing some strings. For now it just fallback to English.

[vherasme]

es-es.yaml Spanish translation is missing some strings. For now it just fallback to English.

Can I improve that translation? Bear in mind however that some English words are so common that they're not translated in some cases. Especially those related to technology

[wait-what]

I don't know if you need this, but I'll add Lithuanian

[fengkx]

@vherasme There are 7 strings didn't have translation in Spanish. I think it would be better to translate it for consistency please.

[dukkee]

@fengkx Added russian #76