Firstly, as you have Windows 10 you could get a spanish-speaking friend to add English to your Windows installation without removing Spanish; you can find the procedure on the web (I’ve never done it myself). Regardless of the interface language you can declare any keyboard you like.
I work in French and English on machines running French Windows. I can choose the LO user interface language on the office machine (Version 5.3.7.2). However, the portable is in a situation like yours, offering LO only in French (it’s Version 5.0.5.2). The English interface is needed for confusing my students and for getting the vocabulary right when discussing bugs and enhancements.
The only explanation I can think of could be that LO on the portable might have been downloaded from the French site https://fr.libreoffice.org/ - I don’t really know because I’m fortunate enough not to notice which language a site is in.
Anyway, unless someone can find the elusive language packs, I’ll wait and see what happens next time I get round to doing an update (from the international LO site…).