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.editor.applyStyle()

[Piotrek Koszuliński]

This is caused by styles system being very inflexible. Styles cannot be configured to handle more cases than just the ones we needed for basic styles, links and similar features.

Other issues can be found in #10742, #10675, #4505.