Nested submenu in Side-Menu

That site is my testing server. You can be sure it's not a Joomla 2.5. It's usually a bit newer than the latest available release. Currently it's on Joomla 3.5 beta
The template there is exactly the same {LESS} Allrounder you can download here. Actually in default configuration without anything changed.

As for the module style suffixes, check the first few modules you see on that page. The positions "beforehead1 bis 3" all have the applied "Suffix" written in it. Same for "afterhead1 bis 3" where the used "Modulklassensuffix" is declared. The last one is "top1 bis 3" with "Modulklassensuffix" "-style6".
You see the suffixes live in effect there.

Hi Again Thomas

Thank You for the detailed explanation.
I'm a bit confused. I have made a clean install of Joomla 3.4.5, and installed Your Allrounder-Template, and not changed anything in the configuration (as far as I know... )
I get the sidemenu as formerly shown, but I will very much like to have the exact same design like the sidemenu on Your Site sermon.hopto.org/index.php/de/sermons

I will very much apreciate if You can explain what I have to do for getting it right, or what I eventually have missed.

Thank You Again in Advance

Hi Thomas

I'm so sorry. I found what I have messed up. I have created a new Sidemenu-Module, and not used the default one supplied with the Template.
I did place the value "_menu" in the wrong paramter, in 'Menu Class Suffix' instead of 'Module Class Suffix'.

By the way, what does the value 'nav-pills' do in the 'Menu Class Suffix' ?

I really apreciate Your patience, and hope You will continue to develop the Allrounder-Template for future Jooomla-releases.

Yep, that explains it

As for the Menu Class Suffix and nav-pills, have a look at the Bootstrap documentation: getbootstrap.com/2.3.2/components.html#navs