In this example the edit numeric field can be set to have "," as decimal separator.
<?php 
require_once '../../../../php/demo/tabs.php';
?>
<!DOCTYPE html>
<html>
  <head>
    <title>jqGrid PHP Demo</title>
    <link rel="stylesheet" type="text/css" media="screen" href="../../../../css/jquery-ui.css" />
    <link rel="stylesheet" type="text/css" media="screen" href="../../../../css/trirand/ui.jqgrid.css" />
    <link rel="stylesheet" type="text/css" media="screen" href="../../../../css/ui.multiselect.css" />
    <style type="text">
        html, body {
        margin: 0;            /* Remove body margin/padding */
        padding: 0;
        overflow: hidden;    /* Remove scroll bars on browser window */
        font-size: 75%;
        }
        
    </style>
    <script src="../../../../js/jquery.min.js" type="text/javascript"></script>
    <script src="../../../../js/trirand/i18n/grid.locale-en.js" type="text/javascript"></script>
         <script src="../../../../js/trirand/jquery.jqGrid.min.js" type="text/javascript"></script> 
        <script type="text/javascript">          
    $.jgrid.no_legacy_api = true;
    $.jgrid.useJSON = true;
    $.jgrid.defaults.width = "700";
    </script>
    <script src="../../../../js/jquery-ui.min.js" type="text/javascript"></script>
  </head>
  <body>
      <div>

          <?php require_once("grid.php");?>
      </div>
      <br/>
      <?php tabs(array("grid.php"));?>
   </body>
</html>
grid.php.
<?php
require_once '../../jq-config.php';
// include the jqGrid Class
require_once ABSPATH."php/PHPSuito/jqGrid.php";
// include the driver class
require_once ABSPATH."php/PHPSuito/DBdrivers/jqGridPdo.php";
// Connection to the server
$conn = new PDO(DB_DSN,DB_USER,DB_PASSWORD);
// Tell the db that we use utf-8
$conn->query("SET NAMES 'utf8'");

// Create the jqGrid instance
$grid = new jqGridRender($conn);
// Write the SQL Query
$grid->SelectCommand = 'SELECT OrderID, CustomerID, Freight, OrderDate, ShipCity FROM orders';
// set the ouput format to json
$grid->table = 'orders';
$grid->dataType = 'json';
// Let the grid create the model
$grid->setColModel();
// Set the url from where we obtain the data
$grid->setUrl('grid.php');
// Set some grid options
$grid->setGridOptions(array("rowNum"=>10,"rowList"=>array(10,20,30), "sortname"=>"OrderID","height"=>150));
// Change some property of the field(s)
$grid->setColProperty("OrderDate", array(
    "formatter"=>"date",
    "formatoptions"=>array("srcformat"=>"Y-m-d H:i:s","newformat"=>"m/d/Y"),
    "search"=>false,
    "editable"=>false
    )
);
$grid->setColProperty("OrderID",array("editable"=>false));
//============================================
/*
 *  the unformat is used to put the original values from the DB
 * to the editform.
 * Using custom unformat allow us toreturn the needed value with
 * "," as decimal separator
 */
$unformat = <<<UNFORMAT
function(value,options,cellobj)
{
    var val = value.replace(".",",");
    return val;
}
UNFORMAT;
$grid->setColProperty("Freight",array(
    "formatter"=>"number", 
    "unformat"=>"js:".$unformat,
    "align"=>"right",
    "editrules"=>array("number"=>true)
    )
);
//===================================================
$grid->setSelect('CustomerID', "SELECT CustomerID, CompanyName FROM customers");
// Enable navigator
$grid->navigator = true;
$grid->setNavOptions('navigator', array("del"=>false,"excel"=>false,"search"=>true,"refresh"=>false));
$grid->setNavOptions('edit', array("height"=>"auto","dataheight"=>"auto", "width"=>"auto"));
$grid->setNavOptions('add', array("height"=>"auto","dataheight"=>"auto","width"=>"auto"));

//==========================================================
/* We use beforecheckvalues to reformat the value readable
 * in the database. This value is changed before it is checed and posted
 * to the server
 * Using this event allow us to test if the value is number and etc.
 * 
 */
$beforecheck = <<<BEFORE
function(postdata)
{
    postdata['Freight'] = postdata['Freight'].replace(".","").replace(",",".");
    return postdata;
}
BEFORE;
$grid->setNavEvent("edit", "beforeCheckValues", $beforecheck);
$grid->setNavEvent("add", "beforeCheckValues", $beforecheck);
//============================================================
// Enjoy
$grid->renderGrid('#grid','#pager',true, null, null, true,true);
?>