This python module provides an API with data about glyph sets for many different scripts and languages. This was crafted to specify the sets of characters that fonts in the Google Fonts collection are expected to provide glyphs for.
If you are a font developer or typeface designer, see the GF Glyphsets WIP subdirectory which provides glyphset definition "standards" that are typically useful sets to draw.
On the other hand, the nam files on the Lib/glyphsets/encodings directory are probably more useful for expert web developers. Those files explain how the Unicode Range subsets are defined, typically per script (writing system), in the Google Fonts css API.