A little over a year ago I translated much of the handbook into Spanish and did a poor job. Thankfully people like Federico went behind me and improved these translations. There were several pages with far too much technical information that I didn't even attempt to translate them and they are still in English in the current version 3 handbook. If someone could translate these pages it would be useful when I can answer questions by attaching a link. Currently I tell the Spanish speaker to translate it themselves and ask me to clarify what they still don't understand.
Pages I know I've used include:
https://musescore.org/es/node/278568 (MIDI import)
https://musescore.org/es/node/278640 (command line options)
but all pages should be translated. I remember seeing a page that has several paragraphs that were not translated but I don't remember which one that was.