In the last days, i searched desperated for a way to enable localisation in combination with MVC and dynamic loading. I found two solutions which were not really comfortable and finally i implemented a way by myself. Because it seems, that many people search a solution for this problem, i will post my way here.

First, i defined a own base controller for my app which has a slightly changed "onClassExtended" method.
Code:
Ext.define('dnes.app.Controller', {
    extend: 'Ext.app.Controller',
    onClassExtended: function(cls, data, hooks) {
    var className = Ext.getClassName(cls),
    match = className.match(/^(.*)\.controller\./),
    namespace,
    onBeforeClassCreated,
    requires,
    modules,
    namespaceAndModule;
        
    if (match !== null) {
        namespace = Ext.Loader.getPrefix(className) || match[1];
        onBeforeClassCreated = hooks.onBeforeCreated;
        requires = [];
        modules = ['model', 'view', 'store', 'locale'];


        hooks.onBeforeCreated = function(cls, data) {
        var i, ln, module,
        items, j, subLn, item;
        
        for (i = 0,ln = modules.length; i < ln; i++) {
            module = modules[i];
            namespaceAndModule = namespace + '.' + module + '.';


            items = Ext.Array.from(data[module + 's']);


            for (j = 0,subLn = items.length; j < subLn; j++) {
            item = items[j];
            // Deciding if a class name must be qualified:
            // 1 - if the name doesn't contains at least one dot, we must definitely qualify it
            // 2 - the name may be a qualified name of a known class, but:
            // 2.1 - in runtime, the loader may not know the class - specially in production - so we must check the class manager
            // 2.2 - in build time, the class manager may not know the class, but the loader does, so we check the second one
            //       (the loader check assures it's really a class, and not a namespace, so we can have 'Books.controller.Books',
            //       and requesting a controller called Books will not be underqualified)
            if (item.indexOf('.') !== -1 && (Ext.ClassManager.isCreated(item) || Ext.Loader.isAClassNameWithAKnownPrefix(item))) {
                requires.push(item);
            } else {
                if(module == 'locale' && typeof document._application_language != 'undefined') {
                requires.push(namespaceAndModule + item + '.' + document._application_language);
                } else {
                requires.push(namespaceAndModule + item);
                }
            }
            }
        }


        Ext.require(requires, Ext.Function.pass(onBeforeClassCreated, arguments, this));
        };
    }
    }
});
Now all my controllers extend this new base controller, what gives me the possibility to define "locales" which is an array with the language files, i want to load.
Code:
Ext.define('dnes.controller.user.User', {
    extend: 'dnes.app.Controller',
    views: ['user.Register'],
    locales: ['user.Register'],
    onLaunch: function(app) {
    ...
    }
});
Then i just need to put the language files in the right directory. For the example above, this would be "locale/user/Register/". The name of the language files have to be the name of the language they define. For english it would be "en.js"
Code:
Ext.define('dnes.locale.user.Register.en', {
    override: 'dnes.view.user.Register',
    title: 'Register new user',
    account: {
    label: 'Account data',
    username: 'Username',
    usermail: 'Email',
    password: 'Password'
    }
});
As you can see, each language file defines a class fitting to its path and overrides the class which uses the language definitions. The view in this case looks as following.
Code:
Ext.define('dnes.view.user.Register', {
    ...
    initComponent: function() {
    var me = this;
    
    me.items = [{
        xtype: 'fieldset',
        defaultType: 'textfield',
        title: me.account.label,
        items: [{
        fieldLabel: me.account.username,
        name: 'user_name',
        allowBlank: false
        }, {
        fieldLabel: me.account.usermail,
        name: 'user_mail',
        allowBlank: false 
        }, {
        fieldLabel: me.account.password,
        name: 'user_pass',
        allowBlank: false,
        inputType: 'password'
        }]
    }];
    
    me.callParent();
    }
});
At last i just need to define the language code for the language, i want to load. That can be done by a specialised function or in a script tag on page load. All what have to happen is, that anywhere before your application, you define document._application_language = 'en'; where you relace 'en' by the language code, you want to load. Now the ClassLoader load the defined "locales" as requires after all other components like stores, models and views are loaded but before the views are rendered.

I hope, this solution helps anybody and you like it.

Lilu