For your language records not to be lost during the plugin deletion you should export them. For that go to the admin panel through the following URL <domain>/admin/languages/mod, and click Export.

In the table that will appear choose the line with your plugin name, and click Export selected. Save the archive to your computer. After installing the plugin you should follow the same URL and import your archive to restore languages.

You can make language import automatic during the plugin installation. For that rename your language archive to langs.zip and add it to the root folder of your plugin. After that add the following line to install.php file:

OW::getLanguage()->importPluginLangs(OW::getPluginManager()->getPlugin('<pluginkey>')->getRootDir().'langs.zip', '<pluginkey>');

Now languages will be automatically imported during plugin installation.