In reply to Jeff Chandler.

You can always just check the theme's "Theme Tags" as it's the official way of declaring support for certain features in themes.

i.e. rtl-language-support, translation-ready, etc

e.g. Justin's Stargazer theme has the followings tags:

custom-background, custom-colors, custom-header, custom-menu, editor-style, featured-images, left sidebar, one-column, post-formats, responsive-layout, right sidebar, rtl-language-support, theme-options, threaded-comments, translation-ready, two columns

As seen on the .org repo page https://wordpress.org/themes/stargazer