Download WordPress theme/plugin translations and apply them to your site manually even their language pack haven't been released or reviewed on translate.wordpress.org
A premium or private plugin isn't available in translate.wp.org, so clicking on the update link will always be a dead end.
A first option might be to just check if the plugin exists in the wp.org and only show the Update Translation if the plugin exists in the directory.
A second option, might be an option to add a particular link to a GitHub or custom/premium repo, as it happens in the settings of GP Auto Extract plugin.
A premium or private plugin isn't available in translate.wp.org, so clicking on the update link will always be a dead end.
A first option might be to just check if the plugin exists in the wp.org and only show the Update Translation if the plugin exists in the directory.
A second option, might be an option to add a particular link to a GitHub or custom/premium repo, as it happens in the settings of GP Auto Extract plugin.