70% accuracy quite easily (between romance languages, anyway. It really sucks for Japanese or Russian, for example
When translating into a native toungue, it's better than 70% accuracy, when minor human filtering is used. It's not perfect, and there are lots of idioms it will miss, but, amazingly, the global world has fixed much of that. A green joke (Spanish) is an off-color joke (English), and someone "should" be able to figure out the meaning from context. A "dark horse" in a contest is a "black horse" in Chinese. Someone should be able to figure that out as well, right?
Translation will always work best into one's native language. The translations fail at making it sound natural. Often because things are untranslatable. Like from between Chinese and English. You don't say "no" in Chinese. You say "Yes, but I can't". But saying that in English would not be direct enough, and would imply some lack of conviction that isn't there. But "no" indicates a lack of politeness. I would love to see translations translate and transliterate. So it says:
"Portugal is the dark horse" (translation)
"Portugal is (the) black horse" (transliteration)
Conferring both the meaning and the tone requires a re-write, not a simple translation. But giving the literal translation and the meaningful one helps with that. At least with more than tourist words. "Where's the toilet?" loses little in translation in any language.