The manage subscriptions link appearing on the Thank You page for one-time products is expected behavior. The feature to 'Manage subscriptions after checkout' has two limitations - inability to translate the text and the manage subscriptions link will appear on Thank You page regardless of purchase type (one-time or subscription). 

You can enable or disable this feature in the Recharge merchant portal: 

1. In the merchant portal click Storefront, then select Customer Portal. 
2. Under Checkout settings, select Disable manage subscriptions at checkout. If the feature is not enabled, the option to enable will be presented in the same location. 
   

If you would prefer to adjust the language used on this field rather than disable the button you can do so in your Shopify theme settings.