Add lsphp73-intl to Debian 11

#1
I have an application that is forcing me to stick with PHP 7.3.

I compiled PHP 7.3 in Openlitespeed.

Now I'm trying to install Roundcube and can't because of the missing PHP intl extension.

How can I add this extension to Debian 11? The repositories start at PHP 7.4.
 
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