I used to work with a guy who was stationed in West Germany during the Korean War. He was still giggling about it as late as 2003 (when we were both caught up in layoffs).
ETA: When we went to Puerto Rico, the freeways has signs that said SALIDA. I knew perfectly well what they meant, but I had to joke, ‘Man, Puerto Ricans eat a lot of salad!’
This stirs up fond memories of one of those little time bombs that nasty big brothers tend to plant in our minds, in the most convincing of words, only to be exposed years or decades later.
When I was 10 or 11, my brother’s friend went to Germany with his family, and in a pre-arranged plan, he brought back a neat switchblade knife for my brother.
It was super cool, with green pearlescent handles, and the classic Italian stiletto styling.
My brother would take it out and flip it open and closed, telling me about its various features as I gazed on in envy. One thing he pointed out was the manufacturer’s name: Rostfrei. He explained how Rostfrei was well known as a maker of high quality German knives.
Over the years (and decades) I had always kept that name in mind, remembering it was a sign of fine cutlery.
Occasionally I would encounter knives at a knife shop that had the “Rostfrei” stamp, and would think “Ah yes! Rostfrei! Good stuff.”
I began to notice the occasional cheap crappy knife bearing this stamp and simply put it down to “darn, the Rostfrei quality is slipping…like everything else in life.”
It wasn’t until I was well in my thirties before I smelled a rat and looked up the word.
“Stainless Steel” 
It took me a couple weeks in Hungary to figure out what a “legjobb” was. I saw the words in shop windows everywhere, it seemed. I was pretty sure a Finno-Ugric language hadn’t randomly borrowed a Germanic word for some kind of freaky bedroom move. (Though, to be fair, those words do sometimes cross linguistic boundaries.) Turns out it just means “best.” As in: leg- (superlative prefix) + jó (“good”) + -bb (comparative suffix). The most good.
Hmm, which one should I apply to?..
Ha! It took me a second because I do understand very basic German, but when I switched back to monolingual English mode, I chortled.
Literally “rust free.”
You can get this even in your own country - a couple of decades ago when I worked in Manhattan, walking to Penn Station, I would see signs in a lot of shop windows and would wonder who this Al guy is who is running for Mayor.
“AL POR MAYOR” = Wholesale
I once heard a probably apocryphal tale about how a good old boy bullshitted a bunch of people from out of state about how the Frontage (pronounced in a mock-French style) family was very popular in Texas, and how they were great philanthropists and so forth, as a tale to explain why there were so many roads named “Frontage Road” in Texas.
(hint: that’s what the access roads are labeled as on Texas highways)
When you drive on one-lane-each-way roads in hilly ruralia, there are lots of blind curves and rises and dips where the road has been carved into or through a hill. At each one there is a sign “DO NOT PASS”.
I used to joke that when old Colonel DoNot of the US cavalry was scouting this terrain back in the 1800s, he named every pass he came to after himself. The guy was a regular narcissist.
This Way to the Egress 
“Assmann” is a common second name in Germany. “Ass” in German means “ace”.
We never did find the way to Ausfahft. 
It’s uncommon enough in North America that it got Dick Assman of Regina, Saskatchewan, on the Late Show with David Letterman.
Ahhh, Québec, where you need battries for your Walkman. Although today I suppose they’re battries rechargeables. I wonder if Neal Peart could have used those.
I had the same experience in Rome. I kept seeing transit buses that I thought were called Uscita or run by a company by that name. Turns out Uscita is Italian for exit, and that word was over the rear door. It took me two days to figure that out.
Hey! I resemble that remark!!!
Press on
Just the story I was going to mention
There’s a story at my old job about a translation error for an Exit sign. The sign also had the word in Arabic, however it seems that due to a mistranslation or a regional/dialect issue, the selected word read more as “evacuate yourself” and was rather rude.
Québec, where you need battries for your Walkman
Whereas in France, it is also (and how’s this for a faux ami) … piles. (There is a chain of shops called 1001 Piles, though I notice they do now also use ‘batteries’ in some cases)
Probably belongs on the Americanisms/Britishisms thread to be honest, but it makes me laugh every single time I hear it, so I’m going to put it here anyway: fanny pack.