All files in the plugins will be removed and replaced by the new files in the newer versions. So do not keep the language files in the plugin folder. Instead, you can:
Send me the translation files, so I can update the extensions with the new translations! That will help other people!
Or you can keep your translation locally in the wp-content/languages/plugins/PLUGIN-SLUG/ folder. WordPress will use the translation files in this folder if they're available. If you use the Loco Translate plugin to translate the plugins, it has option to save file to this folder.