Babel.locale_selector and Babel.timezone_selector no longer exist. They must be provided
either when the Babel() object is created or when init_app() is called. This is to support
having a single Babel object for multiple Flask apps (#107) as well as to simplify settings
and multi-threaded state.
https://github.com/python-babel/flask-babel/blob/master/CHANGELOG Section 3.0.0
One option would be to temporarily pin flask-babel to
2.0.0
as well.@moridius started working on a proper fix, which gets rid of the decorator.