[Gelöst] install languages

Background of the issue:
I am trying to install languages on my site versteckter Link using WPML. However, I am encountering issues with the language menu constantly switching to Romanian. Additionally, I am seeing multiple error messages related to the Zend OPcache API restriction and header modification issues.

Symptoms:
Warning: Zend OPcache API is restricted by "restrict_api" configuration directive in /data/web/virtuals/370328/virtual/www/domains/hotelcaalvise.eu/wp-content/plugins/wpml-string-translation/StringTranslation/Infrastructure/StringGettext/Command/CreatePhpFileCommand.php on line 26. Warning: Cannot modify header information - headers already sent by (output started at /data/web/virtuals/370328/virtual/www/domains/hotelcaalvise.eu/wp-content/plugins/wpml-string-translation/StringTranslation/Infrastructure/StringGettext/Command/CreatePhpFileCommand.php:26) in /data/web/virtuals/370328/virtual/www/domains/hotelcaalvise.eu/wp-includes/functions.php on line 7168.

Questions:
How can I resolve the Zend OPcache API restriction error?
Why is the language menu switching to Romanian automatically?
How can I fix the header modification error?