Detect language automatically according to browser preferences

[Quenix]

I've noticed that my main browser language is PT-BR but game instance is always loaded in english due to this validation:

messages.languageActive.hasOwnProperty(requestLang)

Because portuguese is added as pt-br and requestLang returns "pt".
Changing it through settings seems fine. I will create a fork to pull request this fix.

[adi-g15]

Just to link it with the PR, so that it shows that it's being worked upon 👍🏽 #182