[v3-alpha] Routing based on locale for docs theme

[davitp]

Hi Nextra Team,

As per the current draft of the v3, to create a multi-locale website one needs to build corresponding folders as follows:

• en
• ru
• etc.

Also, as far as I can see, the default locale is retrieved from the NEXTRA_DEFAULT_LOCALE env variable.
It looks like there is no way to have a default locale without a locale prefix in the route, so, if "en" is the default locale, the path will still be prefixed with /en/ and the locale is just guessed from the first segment of the path.

Is that the plan moving forward?