This article suggests that originally the expression was: "parler français comme un Basque espagnol".
Is this expression correct in English?
It can't be correct or not since it's a proverb. Proverbs may not be very grammatical.
Is there a similar expression which refers to non-native speakers who don't speak the language well, or who have a very pronounced accent?
I'm not aware about direct proverb counterpart in English, so I would suggest translating it by its meaning:
"To speak broken English" — incorrect or awkwardly structured English, usually spoken or written by non-native speakers (Urban Dictionary)
TL;DR: The problem with translating proverbs is need to convey the context. Historically, people are only aware about neighboring nations, and, of course, there are jokes about each other. An average English (or American) reader or listener may not be simply aware what's wrong with Spanish cows (or Spanish Basques). It has changed in a recent centuries, but still not sufficient to understand tiny details of a humorous context.
I don't know who told you that you can't use umpteen before million. M-W's Student Dictionary seems to disagree with that assertion:
umpteen (adj) numerous but not fixed in amount : umpteen million things to do
So, grammatically, I don't find anything wrong with your translation.
That said, umpteen is an informal word in English – note how Macmillan includes an INFORMAL label on its entry. It really depends on the context. If you are talking about how many people died in a war, for example, that might call for a more solemn word than umpteen.
However, there are cases where the word could work. If you are trying to express frustration and exasperation, umpteen might be a word that could do that.
In other words, if a student was writing a historical report about World War II, or a veteran was writing a dedication speech for a WWII memorial, I think:
Umpteen million people died in World War II.
would not be an appropriate sentence to use. However, if someone was giving an
emotional plea for an end to hostilities, then I suppose that word might work:
Umpteen million people have died in this war – when are we going to have peace?
That use of umpteen essentially conveys, "too many to bother to count, but I'm not concerned with the exact number right now – when will we have peace?"
Best Answer
"I know where you are coming from" means that the speaker understand the perspective and the motivation of the other person, even though it may not be obvious.
I'm not a native speaker of Spanish, but from my understanding of the Spanish phrase, I thought it is more similar to the English phrase "I know where you are going with this". While there are similarities, the two phrases are not exactly equivalent. The latter one emphasizes on the other person's intent or conclusion before it has been explicitly stated.