Set Czech (cs) and Slovak (sk) as reciprocal fallbacks
The two languages are mutually intelligible at a very high degree and
most speakers can be considered bilinguals or passive bilinguals.
- Eurostat special eurobarometer 386 (2012). http://ec.europa.eu/public_opinion/archives/ebs/ebs_386_en.pdf
- Mira Nábělková
- http://doai.io/10.1515/IJSL.2007.004: «These differences do not prevent the users of Slovak and Czech from understanding discourse in the other language [...]. While contact with Czech texts in the Slovak environment is obvious, it does not appear to be so in the opposite case.»
- High degree of passive bilingualism even in recent generations who don't feel it much. https://repozytorium.amu.edu.pl/bitstream/10593/9168/1/02_Viera_K0VA%C4%860VA_Czech_Slovak_intercultural_265_280.pdf
- Discussions with several translators.