So, after further investigation I got it working by now. For future ppl who don't want to search around: As said, I implemented a custom loginform based on AbstractUsernameFormAuthenticator. There, in method validateUsernameAndPassword, where in the end the context gets set by context.setUser(user); So, I was particularly interested in the "builtin" field locale, which I added to the client mappers. First try was to add this line: user.setAttribute(UserModel.LOCALE, Collections.singletonList(context.getHttpRequest().getHttpHeaders().getCookies().get("KEYCLOAK_LOCALE").getValue())); BUT: This only seems to work in Firefox, for some reason (didnt investigate further), the KEYCLOAK_LOCALE - Cookie wasn't set in Chrome. So, to make it work I had to add a custom cookie to my custom theme via js, which was pretty straightforward. Now this is working and I get the locale-field populated with the previously chosen value of locale dropdown when internationalization is enabled. Pretty hard way to go before I found all this little things out. Actually, I thought the locale would've been set internally for the user who logs in when logging in, based on the value of the dropdown, so that I could just add the mapper and... works. :) Best regards, Dominik Am 07.03.18 um 11:03 schrieb Dominik Guhr: