ENThe paper deals with Kleinas' linguistic ideas which are encountered in the text of the Grammatica Litvanica (Regiomonti, 1653). At first glance it might seem as if Kleinas had been a supporter of the 'Sarmatian concept' of the Baltic languages. This is, however, a superficial impression, because Kleinas was much more interested in discussing whether Lithuanian is a 'barbarian' language or not (lingvam iftam, qvam barbaram & confufam dixerc piures). Beyond that Kleinas attempted to achieve a better definition of the way in which one might understand the idea that Lithuanian is a 'mixed and confused' language (qvod lingva hsecfil mixta & confufa lingva). Interestingly enough Kleinas operated according to an explicative model (I would like to call it the 'component theory') which may be observed also in Jan Dhugosz and other authors of that time. In the discussion of these and related ideas some differences are to be noted with respect to the linguistic thought of Mikalojus Daukša. In addition it is worth pointing out some features in common with the poet Simon Dach from Königsberg, but perhaps also with the ideas expressed in De Linguae Latinae Elegantia libri sex (1438-1444) of the Italian humanist Lorenzo Valla. The terms of the discussion are referred to and commented on in the paper. The formal side of Kleinas' argumentation is also interesting since he makes use of an original conceptual metaphor (Lingvam Litvanicam [...] liqvore aliantm lingvarum permixtam) which is worth mentioning. [From the publication]