Hi, the plugin already has some languages included as per the following link. Which means that the plugin should be translated to what ever language your site is set to provided the language po and mo files are up to date.
https://translate.ww.wp.xz.cn/projects/wp-plugins/affiliates-manager/
If your language po and mo files are not up to date yet you will need to update the language files yourself unfortunately. We have no control on the translations of the languages the WordPress community so kindly submits to us. The following guide can help you.
https://wpaffiliatemanager.com/affiliate-manager-plugin-translation/
Kind regards.