Spanish language
In Spain and in some other parts of the Spanish-speaking world, Spanish is called not only (Spanish) but also (Castilian), the language from the kingdom of Castile, contrasting it with other languages spoken in Spain such as Galician, Basque, Asturian, Catalan, Aragonese and Occitan.
Mexico
Spanish is the "de facto" national language spoken by the vast majority of the population, making Mexico the world's most populous Hispanophone country. Mexican Spanish is the set of varieties of the language spoken in the country, which differs from one region to another phonetically, syntactically and lexically. In general, Mexican Spanish does not make any phonetic distinction among the letters "s" and "z", as well as "c" when preceding the vowels "e" and "i", as opposed to Peninsular Spanish. The letters "b" and "v" have the same pronunciation as well. Furthermore, the usage of "vos", the second person singular pronoun, found in several Latin American varieties, is replaced by "tú"; whereas "vosotros", the second person plural pronoun, fell out of use and was effectively replaced by "ustedes". In written form, the Spanish Royal Academy serves as the primary guideline for spelling, except for words of Amerindian origin that retain their original phonology such as "cenzontle" instead of "sinzontle" and "México" not "Méjico". Words of foreign origin also maintain their original spelling such as whisky and film, as opposed to "güisqui" and "filme" as the Royal Academy suggests. The letter "x" is distinctly used in Mexican Spanish, which may be pronounced as (as in "oxígeno" or "taxi"), as particularly in Amerindian words (e.g. "mixiote", "Xola" and "uxmal") and as the voiceless velar fricative (such as "Texas" and "Oaxaca").