In the given diagram:
I. Rectangle represents persons who know English.
II. Triangle represents persons who know Marathi.
III. Square represents persons who know Telugu.
IV. Circle represents persons who know Hindi.

The regions labelled from $1$ to $12$ represent various combinations of language proficiency among the individuals.
How many individuals can speak English exclusively?

To find the number of individuals who can speak English exclusively, we need to identify the region that lies solely within the rectangle (representing English) and does not overlap with any other geometrical shape (Triangle, Square, or Circle).
From the given diagram, the region with the number $12$ is located only inside the rectangle and outside all other shapes.

Therefore, the number of individuals who can speak English exclusively is $12$.