How to know the labels assigned by astype(‘category’).cat.codes?

You can generate dictionary:

c = language.lang.astype('category')

d = dict(enumerate(c.cat.categories))
print (d)
{0: 'english', 1: 'spanish'}

So then if necessary is possible map:

language['code'] = language.lang.astype('category').cat.codes

language['level_back'] = language['code'].map(d)
print (language)
      lang         level  code level_back
0  english  intermediate     0    english
1  spanish  intermediate     1    spanish
2  spanish         basic     1    spanish
3  english         basic     0    english
4  english      advanced     0    english
5  spanish  intermediate     1    spanish
6  spanish         basic     1    spanish
7  spanish      advanced     1    spanish