The map below illustrates how the local languages in the Cape Town region have changed throughout the decade from 2001- 2011. OR The map below illustrates how the languages in the Cape Town region have changed throughout the decade, which spans the years 2001 --2011. I changed "had" to "have" in order to keep your verb tense the same throughout your sentence. In your original sentence, "illustrates" and "spans" are present tense" but "had" is past tense. Also, "in the Cape Town region" modifies "languages" so I moved it so that it follows "languages." (...which spans the years..." modifies "decade").

The map below illustrates how the local languages have changed throughout the decade, which spans between the years of 2001 and 2011, in the region of Cape Town. This is correct but a little bit of a wordy sentence The map below illustrates how local languages changed through the decade between 2001 and 2011, in the region of Cape Town.

The map below illustrates how local languages changed in the region of Cape Town [throughout the decade OR between the years] of 2001 to 2011.