Add locale to get_body_class to enable local WordPress themes/plugins to enable different design for locales

[ShinichiN]

I want to suggest that get_body_class adds locales to the body tag.

Would be very nice if WordPress supports locale-en_US, locale-sv_SE or locale-ja as body classes because non-English speakers can submit themes both for English writers and local languages bloggers.
For users who use child themes to optimize a theme to their languages, it would be easier to send pull requests and patches to the original themes.

For example, this blog post by @nao shows us how to optimize English based themes for Japanese blogs.
​http://en.naoko.cc/2015/01/29/optimizing-english-based-wordpress-theme-for-japanese-blog/

One of the basic ideas of this theme "Nu2013" by @nukaga in the WordPress theme repository is that the author wanted to offer Japanese optimized version of TwentyThirteen theme.
​https://wordpress.org/themes/nu2013/

[obenland]

If themes use language_attributes() correctly, they could use an attribute selector to make that determination.

[SergeyBiryukov]

Per comment:3, locale-based styling is already possible:

html[lang="en-US"] body {
	background: #fff;
}

html[lang="ja"] body {
	background: #000;
}