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Video abstract for the article 'The importance of interlinguistic similarity and stable bilingualism when two languages compete ' by J Mira, L F Seoane and J J Nieto (J Mira et al 2011 New J. Phys. 13 033007). Read the full article in New Journal of Physics at http://iopscience.iop.org/1367-2630/13/3/033007/fulltext/. GENERAL SCIENTIFIC SUMMARY Introduction and background. A model is proposed for the case of two languages that compete for speakers in a society without social or spatial structures allowing bilingualism, which enters the model by a parameterization of the similitude among languages. Previous work on the subject, which does not account for bilingualism, arrived at situations where only one language was able to survive in the long term. Here, the simpler situation involving bilingual individuals is adopted, attempting to find a minimalist model that correctly accounts for this phenomenon. The stability of the model is analyzed, seeking situations in which the two languages can coexist. Main results. From analysis of the stability of the model, it is found that the role played by bilingualism enables stable situations in which both competing languages can survive if some conditions (the number of initial speakers, the similitude of the languages and their relative status) are met. The dynamics of Galician and Castilian (spoken in north-west Spain) are closely reproduced by the proposed equations. Wider implications. The model sets up a starting point for modeling situations involving bilingualism. Further research incorporating social- or spatial-based interactions should recover this model with a mean-field approach. The model also offers an easy technique for measuring the similitude of two languages which coexist within a certain community.