For example, in English the word right (opposite of left) and right (privileges, as in human rights) are homonyms. In Spanish, derecho/a also means both of those things. Don’t the concepts behind those words predate the cross-pollination of the two languages? Why do they share this homonym quality?
So that’s why “straight on” and “on the right” are the maddeningly confusable “a derecha” and “en derecho”. Such a pain when following directions.
It could be worse.
That word was originally a verb, it’s the perfect participle of Latin dirigo “to lay straight”, “to direct”, “to steer”. The verb itself kicked the bucket; if it didn’t, it would’ve been something like *dereger in Spanish, with the past participle *derecho.
So “driven straight to the right” would’ve become *“derecho en derecho a la derecha”.
(Thankfully the verb got replaced by its own reborrowed version dirigir “to drive”, “to direct”, so the sentence is a bit less maddening: dirigido en derecho a la derecha.)
[inb4 I’m not a native speaker so if anyone finds a mistake please do tell me out. I’m a bit too prone to portuñol.]