You could also use Forums Censure PRO plugin. You can insert any word or character in the user blocking list of this plugin. Once some word or character is found it'll block the user or just set the post as under moderation:

https://gvectors.com/product/forums-censure-pro/

i wanna block the entire russian alphabet etc and dont want to install a plugin. i know how to code but its hard getting started with wordpress because there isnt a great tutorial available thats not showing how to install another plugin

wpForo Spam Control already removes all URLs of new registered users if you configure it. Just set the value of "Min number of posts to be able to post links" option for example 5 to remove all external URLs from posts of users who don't have at least 5 approved posts yet. The option is located in wpForo > Settings > Spam Control admin page.

i tried the following but its just not working so i assume there is maybe a custom hook for wpforo?

function preprocess_comment_remove_url( $commentdata ) {
    $commentdata = "not a test";
    return $commentdata;
}



// Hook our function to WordPress the_content filter
add_filter( 'preprocess_comment' , 'preprocess_comment_remove_url', 10, 1);