The idea behind it is the question what the Welsh language would have looked like if it had been a Romance instead of a Celtic language : a sister language to French , Spanish and Italian , but one that looks much like Welsh . It plays a key-role in the made-up world of Ill Bethisad , where Latin took the place of Old Celtic as the spoken language of the people in Great Britain , thus giving way to the development of Brithenig . Rather , Brithenig started as a thought experiment to create a Romance language that might have evolved if Latin had displaced the native Celtic language as the spoken language of the people in Great Britain .