Fix date-parsing for non-English locales (again)
Fix date-parsing for non-English locales (again)

The previous fix for Thunderbird 68 to make Send Later determine the
correct locale to parse dates in apparently broke before Thunderbird
68 actually shipped, so an additional fix is called for.

People using Thunderbird in a foreign language that Send Later knows
how to parse should be able to type dates in that language again.

jikamens/send-later,jikamens/send-later,jikamens/send-later,jikamens/send-later