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Your LimeSurvey version: 6.3.8
Own server or LimeSurvey hosting: Own Server
Survey theme/template: n/a
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When installing the CE of Limesurvey I get a red exclamation mark PHP Collate library (language sort order) 
is not installed. That might be so, but how to install it for PHP 7.4? I couldn't find any hint what library this is. Any idea? All the rest is green and the tool itself works well.
 

You can try installing through the commands in base,


Check that you restart your web server after installation and then,

Thank you kindly, that solved, it! 100%.