After a bit of struggling I am making some progress with Editor. I haven't yet figured out one important thing though:
How do I update columns in my database table outside of the Editor form scope??

I tried a few things in Javscript but nothing really works. I don't understand how to use "cell()" because I didn't really find a suitable example - and without examples I am lost ...

I also tried something with "preCreate" (see last statement in the code) but it didn't work and I couldn't get hold of the field I wanted to update "userTable.update_id" was wrong ...

This is my Javascript:

function tblUser() {
    var userEditor = new $.fn.dataTable.Editor( {
        ajax: {
            url: 'actions.php?action=tblUser',
            type: 'POST',
            data: {
                lang: lang
            }
        },
        table: "#tblUser",
        fields: [ {
                label: "Address:",
                name:  "user.title",
                type:  "select",
                options: [
                    { label: "Mr.", value: "Mr." },
                    { label: "Ms.", value: "Ms." }
                ]
            }, {
                label: "Title (if any):",
                name:  "user.acad",
                type:  "select",
                options: [
                    { label: "-", value: "" },
                    { label: "Dr.", value: "Dr." }
                ]
            }, {
                label: "First name:",
                name:  "user.firstname"
            }, {
                label: "Last name:",
                name:  "user.lastname"
            }, {
                label: "Language:",
                name:  "user.language",
                type:  "select",
                options: [
                    { label: "Deutsch", value: "de-DE" },
                    { label: "English", value: "en-GB" }
                ]
            }, {
                label: "Role:",
                name:  "user.role",
                type:  "select",
                options: [
                    { label: "bla", value: "bla" },
                    { label: "blue", value: "blue" }
                ]
            }, {
                label: "Email:",
                name:  "user.email"
            }
        ]
    } );
       
    var userTable = $('#tblUser').DataTable( {
        dom: "Bfrtip",
        ajax: {
            url: 'actions.php?action=tblUser',
            type: 'POST',
            data: {
                lang: lang
            }
        },
        columns: [
            {   data: null,
                render: function ( data, type, row ) {
                    var titleTransl;
                    if (lang == 'de') {
                        if (row.user.title == 'Mr.') {
                            titleTransl = 'Herr';                            
                        } else {
                            titleTransl = 'Frau';
                        }
                    } else {
                        titleTransl = row.user.title;
                    }
                    return titleTransl + ' ' + row.user.acad + ' ' + row.user.firstname + ' ' + row.user.lastname;
                }    
            },
            {   data: "user.title"  },              
            {   data: "user.acad" },
            {   data: "user.firstname" },
            {   data: "user.lastname" },
            {   data: "user.language",
                render: function ( data, type, row ) {
//                  return language == 'de-DE' ? 'Deutsch' : 'English';
                    if (lang == 'de') {
                        if (row.user.language == 'de-DE') {
                            return 'Deutsch';                            
                        } else {
                            return 'Englisch';
                        }
                    } else {
                        if (row.user.language == 'de-DE') {
                            return 'German';                            
                        } else {
                            return 'English';
                        }
                    }
                }    
            },
            {   data: "user.role" },
            {   data: "user.email" },
            {   data: "user.updater_id" },
            {   data: "user.creator_id" }
        ],        
        columnDefs: [
            {   targets: [1, 2, 3, 4], visible: false}          
        ],
        // lastname and firstname ascending
        order: [[ 3, 'asc' ], [ 2, 'asc' ]],
        select: {
            style: 'single'
        },            
        buttons: [
            {   extend: "create", editor: userEditor },
            {   extend: "edit",   editor: userEditor },
            {   extend: "remove", editor: userEditor },
                      "colvis",
            {   extend: "showAll", name: "showAllButton",            
                action: function ( e, dt, button, config ) {                
                    dt.rows({ selected: false }).nodes().to$().css({"display":"table-row"});
                    dt.buttons('showAllButton:name').nodes().css({"display":"none"});
                    //if show all button is clicked, a potential search will be reset and the table is redrawn.
                    if (dt.search() > '') {
                        dt.search('').draw();
                    }
                }
            }
        ]
    } );
    userTable
            .on ('select', function ( e, dt, type, indexes) {
                dt.rows({ selected: false }).nodes().to$().css({"display":"none"});
                dt.buttons('showAllButton:name').nodes().css({"display":"inline", "background-color":"#337AB7", "color":"white"});
            });
         
    userTable
            .on ('init', function ( e, settings, json) {
                userTable.buttons('showAllButton:name').nodes().css({"display":"none"});
            });
    userTable
            .on ('preCreate', function (e, json, data) {
                if (userTable.updater_id < 1) {
                    userTable.updater_id = currentUserId;
                }
            });
}

And this is my PHP. When I found out I couldn't get the JS working I thought I could play around a little with "getFormatter" and "setFormatter". The get stuff worked; it returned spaces - as desired. But it didn't update the database fields with "$id" - I guess because Editor doesn't know that the fields were updated. PLEASE HELP, thanks.

function tblUser(&$db, &$p, &$lang, &$id) {
    if ($lang === 'de') {     
        $msg[0] = 'Feld darf nicht leer sein.';
        $msg[1] = 'Bitte geben Sie eine gültige E-Mail Adresse ein.';      
    } else {
        $msg[0] = 'Field may not be empty.';
        $msg[1] = 'Please enter a valid email address.'; 
    }
    Editor::inst( $db, 'user' )
    ->field(
        Field::inst( 'user.title' )->validator( 'Validate::notEmpty', array('message' => $msg[0]) ),
        Field::inst( 'user.acad' ),
        Field::inst( 'user.firstname' )->validator( 'Validate::notEmpty', array('message' => $msg[0]) ),
        Field::inst( 'user.lastname' )->validator( 'Validate::notEmpty', array('message' => $msg[0]) ),
        Field::inst( 'user.language' )->validator( 'Validate::notEmpty', array('message' => $msg[0]) ),
        Field::inst( 'user.role' )->validator( 'Validate::notEmpty', array('message' => $msg[0]) ),
        Field::inst( 'user.email' )->validator( 'Validate::email', array(
                                                'required' => true,
                                                'message' => $msg[1]) ),
        Field::inst( 'user.updater_id' )    ->getFormatter( function($val, $data, $opts) {
                                                return '';
                                            } )
                                            ->setFormatter( 'Format::ifEmpty', $id ),
        Field::inst( 'user.creator_id' )    ->getFormatter( function($val, $data, $opts) {
                                                if ($val > 0) {
                                                    return $val;
                                                } else {
                                                    return '';
                                                }
                                            } )
                                            ->setFormatter( 'Format::ifEmpty', $id )
    )
    ->process($p)
    ->json();
}