Backdrop CMS does not support the default front page setting to be multilingual (one node for each language). Drupal 7 core does not either, but the contrib module i18n does. This feature would be helpful for Backdrop adoption in multilingual environments
However, there's a small workaround, using the redirect function in node settings. Just add a redirection to the default front page, pointing to the intended 2nd language front page node, and make this redirection language aware (2nd language).
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Hey there! That error message is definitely a head-scratcher. Even though you uninstalled Views, it sounds like something is still referencing a Views-related constant. Maybe a custom module or...
VIEWS_STORAGE_OVERRIDE
Thanks Alejandro. That was the clues I needed.
Ubercart - Programmatically add product to cart and straight to Checkout
Have you tried uc_cart_add_item()? You need to provide the nid of the product. Then you can use backdrop_goto('cart/checkout'); to send the user to the checkout screen. uc_cart_add_item...
Ubercart - Programmatically add product to cart and straight to Checkout