Questions about languages, whether alien, fantasy, or human.
This tag is used for questions that are about language.
This includes alien languages that are commonly found in science-fiction (e.g. Vulcan), as well as fantasy languages (e.g. Elvish).
If your question relates to a human language (e.g. English, Spanish) then this tag is also appropriate. This side-steps any discussion about whether fully-realised languages (e.g. Klingon) is a "fictional language" or not. Questions related to a human language may concern specific details of how SFF works have been translated into other languages (e.g. how Yoda's speech is rendered in official French translations of Star Wars), or about how human languages have developed within the universe of a SFF work (e.g. whether Captain Picard speaks fluent French in-universe).
If your question is more about a human language (e.g. German, French) than about science-fiction or fantasy, or not about a human language within the context of a specific sci-fi or fantasy setting, it might be more appropriate for the English Language and Usage site.