In spite of the importance of the Grand Duchy of Lithuania as a great European power in the Middle Ages and beyond, the Lithuanian language was rarely written down before the 19th century - for a surprising reason. Educated Lithuanians just assumed it was a degraded form of Latin 
Of course, there were other reasons too - the cultural dominance of Polish within the aristocracy after the Union of Lublin, and the stigmatisation of Lithuanian as a peasant language - but the belief that Lithuanian *was* Latin was key
It was common for medieval and early modern historians to trace their nations to spurious Classical origins (e.g. the myth of Brutus in Britain), and the proliferation of Vlachs (Romance speakers) in Eastern Europe made such myths plausible
So early modern commentators on Lithuania essentially assumed that the Lithuanians were Vlachs, descendants of Latin-speakers who had wandered off and got lost in the Baltic forests at the time of the barbarian invasions
Lithuanian does indeed have a strangely latinate feel to it - the language is highly inflected, has a complex grammar, shares some similar noun and verb endings with Latin, and has a lot of familiar-sounding vocabulary. You can even write Lithuanian in dactylic hexameters...
The reason for all this is more primal than any connection with ancient Rome. Lithuanian is a very conservative branch of the Proto-Indo-European language that gave birth to *all* IE languages. It is only distantly related to Latin, yet its archaism makes it look a bit like Latin
The consequence of all this is that educated Lithuanians learnt Latin, often spoke in Latin, and even contemplated imposing Latin on the country *because* they were so proud of the Lithuanian language as a Latin legacy. They recognised Indo-European links but misinterpreted them
So vernaculars do not always get suppressed just because they are considered vulgar or socially undesirable - but also because scholars make wrong assumptions about them
