There is slang which is individual words and phrases. Spanglish just means we start a sentence in English and finish it in Spanish, or the other way around. There are words I did know what they were in English until i was a grown adult, and there are words that even when speaking Spanish is said in english with a half-ass spanish accent. No one from Mexico or Spain cane to northern NM to tell us the right word so we just made it up. both sides of my family are from different parts of northern NM.
My Spanish is even more sucky, I can understand almost everything conversationally. I do have trouble translating at work though as i dont know a lot of academic terms, so that requires google or charades.
I never learned how to properly speak it, (I cant roll my Rs and i suck at vocabulary. My parents didn't make me learn it, as it was better i knew english really well. They know both, but came form the generation where it was common and legal to beat children for speaking spanish in school. So i understand their decision on not forcing me to use it other than talking to family.
My grandpa was bilingual , at the age of 10 him and his older brother were bought out here from Minnesota with the families flock of sheep. His dad found a
local Spanish man to oversee the two boys and flock while he went back to bring the womenfolk an household out in a wagon. Grandpa was fluent in Spanish by the time his dad got back here. I never heard a Spanish word come out of my uncle mouth . But he enjoyed telling how their dad would take grandpa with him everywhere in case he had to talk to any of the locals. And he had lots dealings with the locals because e opened a store when he first got back here then later was involved in local law enforcement.
When the school was built here , it had four classrooms. My grandma had a cow when her oldest boy who was in the second grade came home with his english reader, but could only read it in spanish. His teacher could speak english but had not learned how to read in english. So her students were learning to read english in spanish.
I would come home from school and try to talk to grandpa in what I thought was spanish and he'd tell me to stop talking gibberish that I needed to stick to one or the other, being a know it all kid, I thought he was just being mean.
Now I have a great accent and have been told by lots of gringos that I sound more spanish then a lot of spanish people , but really only know enough real spanish to order a cold beer, marlboro cigs, order food and ask for the bathroom.
I had a step sister who could read spanish but couldn't carry on a conversation in spanish.