If you encounter this 404 error page when you select the language on Switcher, please follow simple steps as the following to solve the problem:
Go ahead Shopify admin > SALES CHANNELS > Online Store > Domains
Select the languages which you want to enable for your Shopify domain
Hope this helps you much.
If you need some more help, please feel free to contact us via live chat or email us at firstname.lastname@example.org