IPS Community Suite supports multiple languages and translation tools such as the Visual Language Editor. Any text your plugin uses should be abstracted to language strings so that your plugin also supports these features.
Language strings are defined as key/value pairs. To add a language string, just open the /plugins/<your plugin>/dev/lang.php file and add an element to the array. Then to use the language string, use this in controllers:
\IPS\Member::loggedIn()->language()->get( 'KEY' );
Or this in templates:
If your plugin creates custom language strings by utilising the IPS\Lang::saveCustom() method, you are allowed to associate them to the core application, but please use an unique key prefix and make sure that all this strings are removed while the plugin uninstallation.