Mention vextwarning flag in manual.html.*

[antongolub]

The vextwarning flag is present in the API, but is not described in manual.html.* ~PR brings descriptions in English (as default for all locales) and Russian, but other langs are needed too. Any help with further translation is appreciated.~

UPD: PR brings descriptions for all locales. Any translation improvements would be appreciated.

• [x] bg
• [x] de
• [x] el
• [x] en (verified)
• [x] es
• [x] fa
• [x] fr
• [x] hi
• [x] it
• [x] ja
• [x] ko
• [x] nl
• [x] pl-PL
• [x] pt-BR
• [x] ro
• [x] ru (verified)
• [x] sv
• [x] uk
• [x] zh-cn

[antongolub]

Behold the Glory of Google Translate)

[antongolub]

@ylafon, could anybody check the correctness of the translation?