Используйте библиотеку
humanize
:
https://pypi.org/project/humanize/
In [1]: import humanize
In [2]: import datetime as dt
In [3]: humanize.naturalday(dt.datetime.now() - dt.timedelta(days=1))
Out[3]: 'yesterday'
In [4]: humanize.naturalday(dt.datetime.now() + dt.timedelta(days=1))
Out[4]: 'tomorrow'
In [5]: humanize.naturalday(dt.datetime.now())
Out[5]: 'today'
In [6]: humanize.i18n.activate("ru_RU")
Out[6]: <gettext.GNUTranslations at 0x5a35478>
In [7]: humanize.naturalday(dt.datetime.now() - dt.timedelta(days=1))
Out[7]: 'вчера'
In [8]: humanize.naturalday(dt.datetime.now() + dt.timedelta(days=1))
Out[8]: 'завтра'
In [9]: humanize.naturalday(dt.datetime.now())
Out[9]: 'сегодня'