Building and maintaining multilingual websites is necessary for organisations and communities trying to increase their global visibility. Such a localisation process might be done in different ways and the structure of a multilingual website should reflect it. However, not clearly understanding localisation patterns in multilingual websites increase the localisation cost. In previous studies, attempts were made to build specific models for multilingual websites but without differentiating between the different possible patterns. In this paper, we present a new formal graph based model, composed of the link structure and of the translation path between the different language versions of a multilingual website. We define some characteristic properties based on this model and derive four localisation patterns. This model was validated through the development of an experimental platform to extract patterns from three multilingual websites with different purposes. The model allowed for a better understanding of localisation patterns in these websites.