how to include other plugin in plugins-compat.php file

Hello,
Hope you are well.
I’m new to WordPress.

Could you tell me how to get string in myCred plugin display in String Translation, same as wordpress-seo? (in steps would be very helpful)

Here is the detail:

I found that you include wpseo_init in include/plugins-compat.php
In order to get string myCred plugin display for translation, do I need to include it the same way, wpseo is add to plugins-compat.php?

If so, do I need to add anything to myCred plug to make it recognize your function?

Then, after adding connection to both plugin, when should I add the following code

if (is_admin())
  pll_register_string('custom translation', 'my string to translate');
else
  echo pll__('my string to translate');

Thanks very much for your help.

https://www.ads-software.com/plugins/polylang/