Languages plugin - can't nest language markup

[Marek Lewandowski]

Issue is reproducable with Chrome/31.0.1627.0, Firefox 23.0, MSIE10

We're unable to nest multiple spans using languages plugin

1. open any sample with CKEditor languages plugin enabled (i.e. samples/replacebyclass.html)
2. Replace content with following HTML: <p>This is sample code.</p>
3. Select sample substring and apply French language (by clicking chinese icon at toolbar, and selecting proper lang).
4. Select is sample code substring and apply Spanish language.

Expected result:
Produced source code: <p>This <span dir="ltr" lang="es">is <span dir="ltr" lang="fr">sample</span> code</span>.</p>

Current result:
Paragraph with nested spans: <p>This <span dir="ltr" lang="es">is sample code</span>.</p>

additional info:

1. Currently spans are created with CKEDITOR.style object being passed to CKEDITOR.editorapplyStyle()