A lot of countries have attempted to eliminate minority languages in favor of the language spoken by the elite, but some were more successful than others. For example, Breton, Occitan, Provençal, Cornish, and pre-Islamic languages in northern Africa have died out or nearly died out, and Irish, Scottish Gaelic, Welsh, and a lot of Native American languages are only still spoken in small areas. On the other hand, Quebec French, Catalan, and the various languages spoken in the Ottoman-ruled parts of the Balkans are still going strong even though their respective governments tried to assimilate them into the majority language. What factors have generally determined whether a government successfully assimilates minority language groups or whether the minority languages survive?
For the record, Provençal is a dialect of Occitan, so the same language.
I can't speak for other languages, but in the case of Catalan, it was a major language before Catalonia got annexed to castille in 1715. Catalan was the language of the administration in both Catalonia and a good part of the Crown of Aragon (basically the kingdom of Majorca and the kingdom of Valencia), as well as a "lingua franca" in the mediterranean (among others) in the XIV to XV centuries, when Catalan maritime codes regulated a good part of the trade in the western mediterranean
https://en.wikipedia.org/wiki/Book_of_the_Consulate_of_the_Sea
the book can be consulted in digital form here:
More information on the Kingdom of Majorca and its influence on mediterranean trade (and the prestige of the language) here:
-Abulafia, David. A Mediterranean emporium: the Catalan kingdom of Majorca. Cambridge University Press, 2002.
So basically, catalan was the language of the administration, the legal system, the literature and of general usage for the people of catalonia for most of their history, that had a large impact on later attempts at language substitution which started in the XVIII century.
After 1715 one important factor in the mantainance of Catalan has been the prestige of the language at a general societal level, and here it is interesting to compare its developement with a similar language, Occitan, which suffered a different fate
-Bratt Paulston, Christina. "Catalan and Occitan: Comparative test cases for a theory of language maintenance and shift." International journal of the sociology of language 1987.63 (1987): 31-62.
Another important factor, I belive not mentioned specifically in the article is the difference between a minority language and a minorised language, a difference which is critical to understand the survivavility of a language. Catalan was minorised (that is, it was increasingly marginalised from the administration, church and public life by force/prohibition) but it was still the language most people used on their everyday lives, so it was by no means a minority language such as Cornish or Bable are. Once the legal repression abated, the language was still able to return to a position of preeminence which it still enjoys today.
-Laitin, David D. "Linguistic revival: Politics and culture in Catalonia." Comparative Studies in Society and History 31.02 (1989): 297-317.
The Catalan government (Generalitat) makes annual reports on linguisitc usage of the catalan population, you can consult it in english here:
http://llengua.gencat.cat/web/.content/documents/publicacions/altres/arxius/EULP2013_angles.pdf
off course there is much more to it than what I wrote, but I tried to mantain it in topic as much as I could, if you have any specific question regarding Catalan I'll do my best to answer it