Good Morning Sebastian.
Further checking for this on a local 17.1 environment, I set the browser language in Spanish.
And the Catalog pages appear in Spanish there after.
And I also see the 'confirmation' message to appear in English.
Although the below shows different:
This string is set/defined in the "catalogbrowse.xml" and some other files (see below).
For the U.S. English language, this file is located in folder:
"%USM_HOME%\view\webapps\usm\locale\icusen\request".
<message>Message:</message>
<success_submit_message>Your request is placed successfully and is under process:</success_submit_message>
For the Spanish language, this file is located in folder:
"%USM_HOME%\view\webapps\usm\locale\iceses\request".
<message>Mensaje:</message>
<success_submit_message>Solicitud enviada correctamente:</success_submit_message>
Kind regards, Louis.