You make a lot of good points here. I haven't read much of Spanish-speaking Poe (partly b/c what little I have read had no translations and I only know like 5 Spanish words >:P), but I agree with the development of language part. I didn't know that it's being called Yavinese, either. I always assumed the planet was uninhabited until the rebels came.
Spanish itself has so many regional variations that I wouldn't be surprised that, even among the fans who feature Spanish-speaking Poe in their works, there's a lot of variety. My guess is that they would generally try to match the Spanish to what Oscar Isaac's family speaks, but the number of fans who can "authentically" write that must be very few. Central and Latin American Spanish is especially complicated b/c words from indigenous languages are also mixed in (and how the words are mixed in depends on the region). It'd be kinda cool to make space Spanish different from Earth Spanish, haha, but it'd take a lot of work.
Anyway, for fandom purposes, I think that noting when a character is speaking another language but still including that dialogue in English is the best way. Besides Poe's possible native language, there are hundreds of others in the SW universe, and they should all be treated the same. Unless you want to highlight a word or phrase (its meaning being difficult to translate to another character, an unfortunate mistake in a language has bad or goofy consequences, etc), then you really don't need to directly include another language at all. Real languages are hard enough w/o worrying about fictional ones, too.
Re: Space Spanish as Yavinese makes no sense
Spanish itself has so many regional variations that I wouldn't be surprised that, even among the fans who feature Spanish-speaking Poe in their works, there's a lot of variety. My guess is that they would generally try to match the Spanish to what Oscar Isaac's family speaks, but the number of fans who can "authentically" write that must be very few. Central and Latin American Spanish is especially complicated b/c words from indigenous languages are also mixed in (and how the words are mixed in depends on the region). It'd be kinda cool to make space Spanish different from Earth Spanish, haha, but it'd take a lot of work.
Anyway, for fandom purposes, I think that noting when a character is speaking another language but still including that dialogue in English is the best way. Besides Poe's possible native language, there are hundreds of others in the SW universe, and they should all be treated the same. Unless you want to highlight a word or phrase (its meaning being difficult to translate to another character, an unfortunate mistake in a language has bad or goofy consequences, etc), then you really don't need to directly include another language at all. Real languages are hard enough w/o worrying about fictional ones, too.