lang = pango.Language(tag$)
tag$ to a Pango language object.
The language tag must be in a RFC-3066 format. Pango language handles
can be efficiently copied (copy the handle) and compared with other
language tags (compare the handle.)
This function first canonicalizes the string by converting it to lowercase, mapping '_' to '-', and stripping all characters other than letters and '-'.
Use pango.GetDefaultLanguage() if you want to get the Pango language for the current locale of the process.