Sven

Problem:
The client is experiencing 500 server errors when accessing the Translation Management settings page in WPML. The issue arises because WPML is searching for a database table with the 'wp_' prefix, whereas the client's site uses a custom table prefix.
Solution:
Follow the steps outlined in the erratum regarding custom database prefixes and multiple languages, which can be found here: https://wpml.org/errata/custom-database-prefix-and-having-a-30-languages-can-cause-a-database-error-when-visiting-translation-dashboard/

If this solution does not resolve your issue, or if it seems outdated, we recommend checking related known issues at https://wpml.org/known-issues/, verifying the version of the permanent fix, and confirming that you have installed the latest versions of themes and plugins. Should you need further assistance, please open a new support ticket at WPML support forum.