Hello Ismael,
Unfortunately we have not the Button Title Attribute on the backed.

If I try the shortcoce methode:
[av_button label='Zur Anfahrtsbeschreibung' link='manually.#/anfahrt' link_target='' size='large' position='left' icon_select='yes' font='entypo-fontello' color='theme-color' custom_bg='#444444' custom_font='#ffffff' av_uid='av-5obiu2i' title_attr='Zur Anfahrt']

I get no arria here:

<a href="#/anfahrt" class="avia-button avia-color-theme-color avia-icon_select-yes-left-icon avia-size-large avia-position-left " style="text-decoration: underline; outline-width: 0px; outline-color: rgb(240, 240, 241); outline-offset: 0px;"><span class="avia_button_icon avia_button_icon_left " aria-hidden="true" data-av_icon="" data-av_iconfont="entypo-fontello"></span><span class="avia_iconbox_title">Zur Anfahrtsbeschreibung</span></a>