Multiple Relations and Contextual Filters in a Translated View
Not sure if there's anything else that could be configured.

Something you could consider is using something like hook_views_pre_view(). Internally then you can check the language of the site for that request, read the values of the month, and using a table, translate internally juillet to july. 


hook_views_pre_view() - https://api.drupal.org/api/drupal/core%21modules%21views%21views.api.php/function/hook_views_pre_view/8.6.x