Use Fluent to localize your Python application. It comes with a Localization class to use, based on an implementation of FluentBundle. It uses the parser from fluent.syntax to read Fluent files.

from datetime import date
l10n = DemoLocalization("today-is = Today is { $today }")
val = l10n.format_value("today-is", { "today": date.today() })
val # 'Today is Jun 16, 2018'

Find the full documentation at https://projectfluent.org/python-fluent/fluent.runtime/.