If you like to play the game in your preffered language do the following

open C:\Users\yourprofile\Documents\My Games\Mafia II Definitive Edition\Data\profiles\76561198004238963 (may be an other number on your side)\settings.xml

Search for the following line

<Language>englisch</Language>

change the name of the language to one of the supported language names

e.g:

<Language>german</Language>

supported names are

englisch
german
french
italian
japanese
korean
latam (maybe for latin american spanisch - not tested)
polishc
russian
chinesesimp
chinesetrad
spanish


You have not to copy any files anywhere. just change the value in your settings.xml.

Thats all to change the language. Maybe the studio will never patch this back in to the ui they have just forgotten about it.

Normally steam should do this when you select a language in the settings dialog.

For my the settings dialog has not worked. So if you run into this problem, too follow this guide to play Mafia II in your lannguage, again.