Sam Bull

Sets the site locale dynamically according to visitor preference. 
This preference comes from the user’s browser.
To install all available translations click the ‘Install All’ button in Settings->General. 
To install individual locales, select the site language and save changes for each locale you want to install.
Technical details: 
 Will parse the Accept-Language HTTP header and find the best matching language for the user from the translations available on the site.

Preferred Locale

Select site locale/language according to user preference (set in their browser).

ShinichiN

“Add More Body Classes” adds classes to the body tag. The tags added are
<ul>
<li>locale-[locale]: ex.) locale-ja for Japanese sites, locale-en-US for default English sites.</li>
<li>page slug: page-slug-[slug]: ex.) page-slug-about for about page.</li>
<li>post type slug: ex.) testimonial-slug-nobil for a singular( ‘testimonial’ ) page with post_name “nobil”.</li>
</ul>

Add More Body Classes

Body tag with more classes such as locale and page slug.

Preferred Locale vs Add More Body Classes