Adding ID or Class to Custom FIeldset (problem with spanish)

Hello,
Custom fieldset grabs the class from the Front End Title, which in the case of spanish can contain an accentuated character, eg. Mercado Público.

In this example, the fieldset has this class: fieldset-mercado-p%c3%bablico

I need to select fieldset classes for adding icons before them.

It could be great to have the chance to add Id or class -or- that the classname is taken from the Admin Title (which doesn’t matter if its spelled right)

Attached: icon added before fieldset