Questions & Answers about Mieszkają w Anglii od roku.
Why does this sentence use the present tense mieszkają when the English translation uses the present perfect "have lived"?
In Polish, if an action started in the past and is still happening right now, you must use the present tense. English uses the present perfect to connect past and present, but Polish simply focuses on the fact that the state is currently ongoing: they live there right now.
Why do we use od roku instead of przez rok to mean "for a year"?
You use od (plus the genitive case, here roku) for an action that is still ongoing. It functions conceptually like "since a year ago". You would only use przez rok if the time period was completely finished and closed, such as if they lived there for a year in the past and then moved away.
What case is Anglii in, and why does it have a double "i" at the end?
It is in the locative case, triggered by the preposition w indicating location. The dictionary form is Anglia. Feminine nouns ending in -ia of foreign origin (like many country names) take the -ii ending in the locative, genitive, and dative cases.
If I wanted to say they lived in England for a year but do not anymore, how would this sentence change?
You would need to change both the verb tense and the time expression to show the action is completed. You would use the past tense of the verb and the preposition przez followed by the accusative case. The sentence would become: Mieszkali w Anglii przez rok.