Scythe is a relatively modern in comparison to neolithic sickle, but it still seems to appear in Western Europe in the mid-Latene period (around 4th century BC). They were most likely well known around 1st century AD in Britain, as specimens found at Newstead and Abington are dated to Flavian era and display characteristics of the Gallic scythe, i.e. they have long, thin blades and have mounting tangs protruding at roughly right angle from the heel of the blade proper. In his "Natural History', Pliny the Elder mentions that there are two popular version of a scythe, a smaller one used by Romans (or rather people living on Italian peninsula) and larger variant used by Gauls. Earliest medieval depictions of scythes follow kind, as seen here: (https://upload.wikimedia.org/wikipedia/commons/thumb/e/e2/Wandalbert_von_Pr%C3%BCm_-_Juli.jpg/800px-Wandalbert_von_Pr%C3%BCm_-_Juli.jpg). This is one of the miniatures adorning a martyrologium written by Wandelbert of Prüm and presented to the emperor Lothar I. This means that it must have been done somewhere between 848 (when the manuscript was finished) and 855 (year of Lothar's death). Given that the reaper with a scythe was made included in the page for July strongly suggests that this tool was already widely used along with the sickle (portrayed on the subsequent illustration).

The second link you provided does not seem to be working (after some tweaking I got the image 9961, but it shows a drawing of a typical scythe, just with an unusually wide blade). But if you're speaking of the scythes with a blade in line with the snaith (haft), much like European voulge or Japanese naginata, this is most likely a 'combat scythe' i.e. a normal farming implement with its mounting bent so that it can be mounted parallel to the haft and used as a makeshift polearm, allthough such use is more common in modern times, with recorded use by the rallied peasants in German Peasant War (1524-1525), the Polish-Swedish War (1665-1660), Vendée War and Kościuszko Uprising (1793 and 1794, respectively) and even as late as January Uprising (1863). There are also mentions of Hussites using makeshift weapons of scythes and other farming implements during Hussite Wars (1419-1436).