Language change involves the competition between alternative linguistic forms (1). Notably, the Spanish past subjunctive comes in two perfectly equivalent variants ended in -ra or -se (2); for instance, in the sentence 'If I were there', the verb can be equally translated to estuviera or estuviese. During a first spontaneous process that began in the Middle Ages, the form -ra migrated from the indicative to the subjunctive, displacing the original -se form (3-5). A second period started with the creation of the Royal Spanish Academy in 1713, which produced a global standardization process that enforced the official spelling of -ra and -se as perfectly interchangeable variants (6). Time series extracted from a massive corpus of books (7) show that this standardization produced a boost in the declining old form -se that eventually faded, leaving -ra as the dominant one in the present time. The time series were successfully fitted by a low dimensional model that integrates two basic collective behaviors: an imitative component, and a fading of collective attention to the institutional regulation. We show that the natural scale over which collective attention fades is inversely proportional to the frequency of use of the verbs.