I like your distinction very much. Given that, I like the use of 'which' as a translation for 'que' here. I suppose it's a little subjective what constitutes a 'very small' field but given that the number of countries is definitely limited, I think that 'which' is a good choice using your criteria. 'Which' is accepted Jan. 19,2020.
Correct, yes. Did you report it? That's how they change things.
Better, no. If it's about ending sentences with prepositions, there has never been a time in English history where grammarians agreed on that prohibition, nor has there been a time when most native speakers avoided the construction.
Generally, English speakers try to front their interrogative pronouns, so one could even argue that the translation DL uses is better.
Regardless, both are perfectly correct.
Not really because all Texans know how to get along! For reading English sentences, it flows better without ending in prepositions. However good novelists to make there writing more believable or provincial end sentences with prepositions as needed. Other novelists wouldn't know the difference.
Regarding a person, conocer can be used more broadly. You can say "Conozco a Denzel Washington" if you know who he is, you don't have to have met him.
However, if you want to mention facts about him, like that he's an actor, you need to use saber: "Sé que Denzel Washington es actor."
Yes. All three. It means to know a person, a city, rather than knowing how to swim. It means to meet someone for the first time. It means to be familiar with. It can be used to mean to visit, later on in the tree are lessons where it is used in the sense of visiting a city as a tourist.
Como castellanoparlante ante la pregunta "Qué países conoces?" podria contestar que todos los del mundo porque los he estudiado en un mapa geopolítico. Pero para traducir como ustedes traducen la frase deberia estar más acotada añadiendo " por haber visitado" o simplemente cambiando el "conoces" por "visitado" En este caso la traduccion seria mejor " What countries do you know".
This isn't at all true. Though it has been repeated by poorly educated English teachers across the United States.
If native speakers use a language in a certain way, then that is literally how the language's usage is defined.
However, even if your prefer references (which are just outdated analysis of native speakers, though less outdated than the past due to the speed at which one can update a webpage vs publishing a new book), look at any grammar reference and it will confirm that it is indeed okay to end your sentence with a preposition. (Webster, Oxford, Grammarly, Grammarmonster, or whichever)
Of these options:
"Which countries are you familiar with?"
"You are familiar with which countries?"
"With which countries are you familiar?"
The first, which ends in a preposition, is by far the most commonly used amongst native speakers around the world.