With ES6 you can do it very easy as below:

var arr1 = new Array({name: "lang", value: "German"}, {name: "age", value: "18"});
var arr2 = new Array({name : "childs", value: '5'}, {name: "lang", value: "German"});
var arr3 = [...arr1, ...arr2];

Output:

    arr3 = [
      {"name":"lang","value":"German"},
      {"name":"age","value":"18"},
      {"name":"childs","value":"5"},
      {"name":"lang","value":"German"}
    ]

You can convert one array into an object and then iterate over the other to combine both. This way you can have O(n) time complexity.

const arr1 = [
    {
        "country_id": null,
        "created_at": "2020-11-13T04:30:16.000000Z",
        "id": 1,
        "updated_at": "2020-11-13T04:30:16.000000Z"
    }
];
const arr2 = [
    {
        "country_id": null,
        "created_at": "2020-11-13T04:30:16.000000Z",
        "id": 1,
        "name": "1111",
        "photo": null,
        "surname": "111",
        "updated_at": "2020-11-13T04:30:16.000000Z"
    }
];
const dictionary = arr2.reduce((acc, curr) => ({
    ...acc,
    ...(curr.id && { [curr.id]: curr })
}), {});

const mappedArray = arr1
    .map(itemFromFirst => ({ 
        ...itemFromFirst, ...dictionary[itemFromFirst.id] 
    })
);

/* Result:
[{
  "country_id": null,
  "created_at": "2020-11-13T04:30:16.000000Z",
  "id": 1,
  "updated_at": "2020-11-13T04:30:16.000000Z",
  "name": "1111",
  "photo": null,
  "surname": "111"
}] 
*/

Here is another way of achieving that goal:

var array = [{
  name: "foo1",
  value: "val1"
}, {
  name: "foo1",
  value: [
    "val2",
    "val3"
  ]
}, {
  name: "foo2",
  value: "val4"
}];

var output = array.reduce(function(o, cur) {

  // Get the index of the key-value pair.
  var occurs = o.reduce(function(n, item, i) {
    return (item.name === cur.name) ? i : n;
  }, -1);

  // If the name is found,
  if (occurs >= 0) {

    // append the current value to its list of values.
    o[occurs].value = o[occurs].value.concat(cur.value);

    // Otherwise,
  } else {

    // add the current item to o (but make sure the value is an array).
    var obj = {
      name: cur.name,
      value: [cur.value]
    };
    o = o.concat([obj]);
  }

  return o;
}, []);

console.log(output);