Pass a nested array to the params argument inside Craft's url() function
Yeah, looks like Craft's url() method doesn't support nested array syntax for querystring params.

If you still want to use it, then you'd need to flatten it with unique keys such as:

Array
(
    [q] =&gt; 
    [cat] =&gt; 
    [city0] =&gt; 28
    [city1] =&gt; 26
    [sort] =&gt; asc
    [order] =&gt; name
)


Alternatively you can manually build the URL yourself in Twig in whatever format you'd like.