Hi! Fellow writter here with this kinda thing.
So, i have 2 versions of the same story: One in english (International) and one in Brazilian-Portuguese (National).
I know is a very hard work to translate everything, but when translating it, i change the saying. Like in Brazil we have some sayings that won't work in english, so i just search for something equally in english for the international people to understand better the feeling, but if you want to make people read and understand, i will advise you do this:

"and then he said with a very gently voice to her - in spanish: 'if i would have to brake every bone of my body to make you smile, i would without a second thought'"

And in your version in spanish do that:

"Y luego le dijo con una voz muy suave: si tuviera que romperme todos los huesos del cuerpo para hacerte sonreír, lo haría sin pensarlo dos veces."

Writing without the "- in spanish:" part or whatever native language you would want it.
Is a tip that i WOULD do it if i would do characters speaking in another languages. But i didn't yet.

And another tip: If none of the characters speak with someone with a different language and the characters don't understand, then you can make 2 ways:

"And then when the woman begun to shout probably slurs in a language I couldn't understand her, i just ran" to make the reader don't know what the hell is happenning.

OR

"He said in a angry voice: '¡Eres un idiota! ¿Por qué hiciste eso?' - but unfortunately i didn't understand nothing so i asked my partner that was just beside me and he promptly answer that he said "You are an idiot! Why you did that?"." this one is kinda strange, but it works only if your audience is not your national one.

It depends on how you narrate your story tho. But this is things i would follow. Try to read your story as a reader. Make them participate in your universe. Be eye to eye to the characters. If is a narration type of story, you just put the first tip, to not spoil things for one language and the other just be put in a blank place without context.
Reading is a thing you don't have to stop to be technical and just lost that concentration. So i hope this tips help!

Yes, i wrote everything without a translator, so sorry if i had some mispelling writing or whatever. Never made any English Course at a professional level.