The URISearchParams API will handle this case cleanly.

It will also do any escaping of the data that is required to make the values or keys URL safe (in your particular example this doesn't matter, but it is worth paying attention to for the general case).

// Create an object to describe the data in the query string
var query = new URLSearchParams();

// Add the languages
var languages = [1,2,3,4,5]
languages.forEach(function (language) {
    query.append("language", language);
});

// Explicitly convert to a string
console.log(query.toString());

Note there is limited browser support at present, so you will probably wish to use a polyfill.

$http(
  method: 'GET',
  url: '/items',
  params: {
    id: JSON.stringify(ids) // ids is [1, 2, 3, 4]
  }
)

That depends on what the target server accepts. There is no definitive standard for this. See also a.o. Wikipedia: Query string:

While there is no definitive standard, most web frameworks allow multiple values to be associated with a single field (e.g. field1=value1&field1=value2&field2=value3).^[4][5]

Generally, when the target server uses a strong typed programming language like Java (Servlet), then you can just send them as multiple parameters with the same name. The API usually offers a dedicated method to obtain multiple parameter values as an array.

foo=value1&foo=value2&foo=value3

String[] foo = request.getParameterValues("foo"); // [value1, value2, value3]

The request.getParameter("foo") will also work on it, but it'll return only the first value.

String foo = request.getParameter("foo"); // value1

And, when the target server uses a weak typed language like PHP or RoR, then you need to suffix the parameter name with braces [] in order to trigger the language to return an array of values instead of a single value.

foo[]=value1&foo[]=value2&foo[]=value3

_GET["foo"]; // [value1, value2, value3]
echo is_array($foo); // true

In case you still use foo=value1&foo=value2&foo=value3, then it'll return only the first value.

_GET["foo"]; // value1
echo is_array($foo); // false

Do note that when you send foo[]=value1&foo[]=value2&foo[]=value3 to a Java Servlet, then you can still obtain them, but you'd need to use the exact parameter name including the braces.

String[] foo = request.getParameterValues("foo[]"); // [value1, value2, value3]

A GET request places your values in the URL in the form:

page.php?arg1=value&arg2=value2

So you cannot just pass an associative array unless you somehow convert it to a string value (maybe in Json format, as antisanity suggested).

Another option may be to pass each key of the dictionary as a URL parameter.

var urlParams  = {
    action: 'process_data',
    get: 'social_popup',
};

for (key in social_buttons_array) {
    urlParams[key] = social_buttons_array[key];
}

$.get(ajaxurl, urlParams, function(data) {
  $('.result').html(data);
});

Which will send something like this:

page.php?action=process_data&get=social_popup&google=0&twitter=0&twitter_follow=0&facebook=0

It really depends how you are going to process that data on the server side.

Express exposes the query parameter as an array when it is repeated more than once in the request URL:

app.get('/', function(req, res, next) {
   console.log(req.query.a)
   res.send(200)
}

GET /?a=x&a=y&a=z:
// query.a is ['x', 'y', 'z']

Same applies for req.body in other methods.

GET request does not have message body, so you can't use GET with contentType: 'application/json; charset=UTF-8'. When you use json in GET request, browser breaks your json and append each josn key value to the url(even if you use JSON.stringify method). Therefore for using json and REST you need to use POST method.