Old and Middle Dutch
The Old Dutch (Oudnederlands) language was spoken between the 6th and 11th centuries, continuing the earlier Old Frankish dialects.
Middle Dutch (Middelnederlands) is a collective name for closely related dialects which were spoken and written between about 1200 and 1550.
The international language in the Middle Ages was Latin, used by church and government. The people spoke the vernacular -then called Diets (pronounced: "Deets", which later became "Dutch")-, but a general unified Dutch language did not yet exist. Each region had its own dialect, but they were all highly mutually intelligible. However, the spelling was not fixed and words were written as they were pronounced; slightly differently in (and within) each dialect. Gradually, the importance of the vernacular increased and the first vernacular Dutch texts appear at the end of the 12th century.
It is important to realize that the modern notion of borders and countries with its own language, culture and population was practically non-existent in the Middle Ages. The borders that were in Europe had everything to do with the influence of certain noble families and were no cultural or language boundaries.
Dutch Language in Cleves
The Dutch influence in the northern part of the Lower Rhine region -Cleves area- was intensive and prolonged. Their Cleves (Kleverlands) dialect -next to the Flanders, Brabant and Holland dialects- was one of the key components of Middle Dutch. The Dutch language was so entrenched there, that the Cleves government and school system continued using Dutch until the 1820s, whereas it remained the church language until the mid 19th century. For all intents and purposes Kleverland (the Land of Cleves) was Dutch.
Modern Dutch Language
In 1618 a further important step was made towards a unified language, when the first major Dutch Bible translation was created that people from all over the region could understand. It used elements from the main dialects.