Read this: The other usage refers to a language that is socially subordinated to a regional or national standard language, often historically cognate or related to the standard language, but not actually derived from it. In this sense, unlike in the first usage, the standard language would not itself be considered a "dialect," as it is the dominant language in a particular state or region, whether in terms of social or political status, official status, predominance or prevalence, or all of the above. Meanwhile, the "dialects" subordinate to the standard language are generally not variations on the standard language but rather separate (but often related) languages in and of themselves. For example, most of the various regional Romance languages of Italy, often colloquially referred to as Italian "dialects," are, in fact, not actually derived from modern standard Italian, but rather evolved from Vulgar Latin separately and individually from one another and independently of standard Italian, long prior to the diffusion of a national standardized language throughout what is now Italy. These various Latin-derived regional languages are therefore, in a linguistic sense, not truly "dialects" of the standard Italian language, but are instead better defined as their own separate languages. Conversely, with the spread of standard Italian throughout Italy in the 20th century, various regional versions or varieties of standard Italian developed, generally as a mix of the national standard Italian with local regional languages and local accents. These variations on standard Italian, known as regional Italian, would more appropriately be called "dialects" in accordance with the first linguistic definition of "dialect," as they are in fact derived partially or mostly from standard Italian. 

Which language spread throughout Italy during the 19th century?
What is the answer? (If it cannot be answered, return "unanswerable")
unanswerable