Cannot change language on 'Personal info' page


Hi all,

This week we installed NextCloud 15 on a CentOS 7 server. I got NextCloud working but all pages are in English. That’s fine for me but my users are Dutch. When a user chooses a different language from English on his/hers ‘Personal info’ page, e.g. ‘Nederlands’, using the drop-down on that page, the right value will be shown, but the laguage setting will not really change. It will remain English. Some other fields on the ‘Personal info’ page also will not retain the values that were filled in (e.g. ‘Phone number’ field, ‘Locale’ field). BTW the only way to change the ‘Locale’ field was by editting config.php (‘default_locale’ => ‘nl_NL’).
It looks like the values in most of the fields on the Settings page are not saved in the database (MariaDB). Are some of the fields saved elsewhere? how could we change the language?

Screenshot of my ‘Personal info page’

Contents of the corresponding ‘oc_accounts’ record

Is there a way to get this problem solved?

Thnx in advance.

Our configuration:
CentOS 7
DirectAdmin 1.55.0
Apache 2.4.38
MariaDB 10.2.22
PHP 7.2.15
NextCloud 15.0.5