Plugin Author
Tim W
(@timwhitlock)
Loco Translate is a PO file editor. Your menu strings are presumably entered into WordPress admin by you. Translating them can’t be done with this plugin.
See https://localise.biz/wordpress/plugin/faqs/translating-posts
You might consider using WordPress multisite. Each WordPress site has one language and its own menu settings. You would simply enter the translated menu items directly into each site.
If you require a single site that has multiple languages you will have to find another plugin that provides this functionality.