Created [i18n] How to translate i2pd web console to your language (markdown)

[i18n]-How-to-translate-i2pd-web-console-to-your-language.md

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+Translation support for web console was added, so you can translate it to your language.
+
+For translation take [Russian translation](https://github.com/PurpleI2P/i2pd/blob/openssl/i18n/Russian.cpp) code, make copy with your language name as file name, and update strings in it.
+
+In that example will be used Turkmen as target language
+
+# Translation steps
+
+1. Update translation namespace to your language:
+```diff
+ namespace i18n
+ {
+-namespace russian // language
++namespace turkmen // language
+ {
+```
+
+2. Update plural form function using information from https://localization-guide.readthedocs.io/en/latest/l10n/pluralforms.html:
+```diff
+ 	// See for language plural forms here:
+ 	// https://localization-guide.readthedocs.io/en/latest/l10n/pluralforms.html
+ 	static int plural (int n) {
+-		return n%10==1 && n%100!=11 ? 0 : n%10>=2 && n%10<=4 && (n%100<10 || n%100>=20) ? 1 : 2;
++		return n != 1 ? 1 : 0;
+ 	}
+```
+
+3. Update translatable strings and numeric strings in plural form:
+```diff
+ 	static std::map<std::string, std::string> strings
+ 	{
+ 		// HTTP Proxy
+-		{"Proxy error", "Ошибка прокси"},
+-		{"Proxy info", "Информация прокси"},
+-		{"Proxy error: Host not found", "Ошибка прокси: Адрес не найден"},
++		{"Proxy error", "Proksi ýalňyşlygy"},
++		{"Proxy info", "Proksi maglumat"},
++		{"Proxy error: Host not found", "Proksi ýalňyşlygy: Host tapylmady"},
+ ...
+ 	static std::map<std::string, std::vector<std::string>> plurals
+ 	{
+ 		// ShowUptime
+-		{"days",    {"день", "дня", "дней"}},
+-		{"hours",   {"час", "часа", "часов"}},
++		{"days",    {"gün", "gün"}},
++		{"hours",   {"sagat", "sagat"}},
+ ...
+```
+
+4. Add language namespace in i18n header file [`I18N_langs.h`](https://github.com/PurpleI2P/i2pd/blob/e412b17f709af249ffa20a08cb111090631e8d0e/i18n/I18N_langs.h#L61):
+```diff
+ 	namespace english { std::shared_ptr<const i2p::i18n::Locale> GetLocale (); }
+ 	namespace russian { std::shared_ptr<const i2p::i18n::Locale> GetLocale (); }
++	namespace turkmen { std::shared_ptr<const i2p::i18n::Locale> GetLocale (); }
+ ...
+```
+
+and in [`I18N.h`](https://github.com/PurpleI2P/i2pd/blob/e412b17f709af249ffa20a08cb111090631e8d0e/i18n/I18N.h#L22-L23):
+```diff
+ 	inline void SetLanguage(const std::string &lang)
+ 	{
+ 		if (!lang.compare("russian"))
+ 			i2p::context.SetLanguage (i2p::i18n::russian::GetLocale());
++		else if (!lang.compare("turkmen"))
++			i2p::context.SetLanguage (i2p::i18n::turkmen::GetLocale());
+```
+
+5. Add commentary about new added language to [`i2pd.conf`](https://github.com/PurpleI2P/i2pd/blob/e412b17f709af249ffa20a08cb111090631e8d0e/contrib/i2pd.conf#L107):
+```diff
+-## Currently supported english (default), russian and ukrainian languages
++## Currently supported english (default), russian, turkmen and ukrainian languages
+ # lang = english
+```
+
+6. Make pull request with changes