Why is it ridiculous? It is what Luther did with his translation of the Bible, which ultimately served to establish modern High German, strongly based on Eastern Central German (the dialect of Luther's home region), and relegated Bavarian, Alemannic, West Frankish and Low German (Low Saxon) to "popular dialects". It is also what several Croatian and Serbian linguists (most notably
Vuk Stefanović Karadžić) did when they in the mid-19th century standardised the Serbo-Croatian language.
Of course, you don't invent a language from scratch, but base it on an existing local dialect, with some adjustment geared at accommodating other
known dialects (
Shtokavian in the case of the Serbo-Croatian standardisation). Such work being initially done by theologians (Cyril and Method for "Old Church Slavonic", Jan Hus in the case of 15th century Bohemian), later by trained linguists implies that a lot of grammatical complexity may be preserved, even though it may long have got lost in popular dialects. An example is the re-introduction of the 4-case noun flexion system into High German, even though it already had been mostly lost in Low German (which essentially had been simplified similar to English), and at least partly lost (disappearance of the Dative) in colloquial East-Middle German.
Once such a "Church standard" has been introduced, it is promoted via church sermon and monastery schools, the latter typically serving for educating the local elite including court officials and scribes. The spread of literacy in the 18th century, and the emergence of newspapers and public schools during the 19th century provided impetus for a second wave of standardisation via grammars and dictionaries - a process that also took place in most (all?) slavophone countries. The new standard is effectively and quickly spread via schools and media. Germanisation of wide parts of Schleswig, the area around the German-Danish border, during the mid-19th century, e.g. required less than thirty years. A similar and equally fast process can be observed with respect to the spread of French in Alsace after WW II.
As such, I think it is rather daring to try to compare modern Serbo-Croatian, which has at least two times been standardized, to 2000-year old Dacian. The same, btw., applies to Romanian - here, the 1860 switch from Cyrillic to Latin alphabet at the same time replaced thousands of Slavic words with Latin- and French-based neologisms.
http://en.wikipedia.org/wiki/Transylvanian_School
