Hi,
I don’t know the details of your system, but it looks like the query you are sending after selection includes a taxonomy query against taxonomy ‘localization’.
Perhaps you could include that taxonomy in the initial query. This is what is send now (for France):
tax_query":{"relation":"AND","0":{"taxonomy":"localisation","field":"id","terms":["290"],"operator":"IN"}}
...
If your initial query is created using PHP you can add the taxonomy to it. See the WP_Query documentation:
http://codex.wordpress.org/Class_Reference/WP_Query
If it’s a shortcode, I think it will be difficult. You can include a taxonomy in the shortcode but there’s no way to default it based on the user’s locale:
[mashup query=”post_type=any&posts_per_page=-1&localisation=290″}