Hello,

When I entered the site I saw this: https://gyazo.com/4feeb97692c1f91f753f1c66a0f9c215

When I have reset 404 page in the Theme Settings, the site has got its normal view: https://gyazo.com/f81a8a1f1f33a81b3c0a536a3d17fbc6

Do not try to add the 404 slugs to the custom 404 pages. And check the page content, most likely you have errors in code and it crashes the whole site.

All the strings from the Wishlist are translated in WPML > Strings Translation: https://gyazo.com/1bd5b2c218da808380b828b94272a628

The pages are translated, as usual, the stings in the Strings Translation.

If you have any questions please feel free to contact us.

Best Regards