Complex sentence: Each municipality of the Kingdom is part of (just) one of these four language areas, of which the borders can be changed or corrected only by a law supported by specific majorities of each linguistic group of each Chamber (article 4).
Split into simpler sentences: Each municipality of the Kingdom is part of one of these four language areas only. The borders of the language areas can be changed or corrected only by a law supported by specific majorities of each linguistic group of each Chamber (article 4).