  We study the stability of two coexisting languages (Catalan and Spanish) in
Catalonia (North-Eastern Spain), a key European region in political and
economic terms. Our analysis relies on recent, abundant empirical data that is
studied within an analytic model of population dynamics. This model
contemplates the possibilities of long-term language coexistence or extinction.
We establish that the most likely scenario is a sustained coexistence. The data
needs to be interpreted under different circumstances, some of them leading to
the asymptotic extinction of one of the languages involved. We delimit the
cases in which this can happen. Asymptotic behavior is often unrealistic as a
predictor for complex social systems, hence we make an attempt at forecasting
trends of speakers towards $2030$. These also suggest sustained coexistence
between both tongues, but some counterintuitive dynamics are unveiled for
extreme cases in which Catalan would be likely to lose an important fraction of
speakers. As an intermediate step, model parameters are obtained that convey
relevant information about the prestige and interlinguistic similarity of the
tongues as perceived by the population. This is the first time that these
parameters are quantified rigorously for this couple of languages. Remarkably,
Spanish is found to have a larger prestige specially in areas which
historically had larger communities of Catalan monolingual speakers. Limited,
spatially-segregated data allows us to examine more fine grained dynamics, thus
better addressing the likely coexistence or extinction. Variation of the model
parameters across regions are informative about how the two languages are
perceived in more urban or rural environments.
