In the sentence, "I will call you when I will get back from visiting my sister," what is incorrect?

The correct response focuses on the phrase "will get" within the context of the sentence. In English, when expressing a future action that is dependent on another future action, the future tense ("will") is used only in the main clause. This means that in the subordinate clause "when I will get back," the use of "will" is unnecessary and incorrect. Instead, the correct form should simply be "when I get back," as the action of getting back will happen in the future but does not need the "will" since it is being connected to the future action of calling.

This construction is a common grammatical rule where the future tense is omitted in subordinate clauses that are introduced by 'when' or similar conjunctions, thereby simplifying the statement and maintaining correct tense agreement.