Yes, absolutely! The primary purpose of tags is to convey areas of expertise, to allow experts to quickly filter questions that are within their area of expertise. Thus Stack Overflow uses programming languages as its primary set of tags, Super User uses operating systems and applications, , History uses geographical areas and historical periods, etc.
The experts in literature are professors of literature. So how are university departments organized? Let's look at a few examples:
- Harvard splits literature among the following departments: Classics, Comparative literature, English, Celtic languages and literatures, Germanic languages and literatures, Romance languages and literatures, etc.
- Oxford has a Faculty of Classics, a Faculty of English Language and Literature, a Faculty of Medieval and Modern Languages which itself is subdivided in sub-faculties by languages and groups of languages.
- Paris-Sorbonne has “French and comparative literature” and a number of faculties for language and literature of linguistic groups (English, Arabic and Hebrew, Germanic and Nordic, Iberic and Latin American, Italian, Slavic).
Clearly “my language” is an important category, and “not my language” gets subdivided into language families. A given professor is usually an expert in the literature of a specific language. So languages are a primary classification for experts. (Time periods are another.)
The bulk of the participants on this site are readers. Many books aren't even translated, and most people are best read in the language that they are most fluent in. So for readers, too, language tags are important.
So absolutely, yes, we should use a language tag on almost every question. This is, in fact, very similar to the use of programming language tags on Stack Overflow. french-literature on this site means any question about French literature, i.e. any question about a book that is part of French literature, just like
java on Stack Overflow means a question about a program in Java and not “a question that is directly related to the specific language”.