I regularly see non-English .com domain names coming up for sale at auction. I took Spanish for a few years in high school, but my foreign language skills are quite atrocious. That being said, because there may be value in non-English .com domain names, it is important to know how viable a name is before bidding on it or agreeing to buy it.
The first thing I do is a Google translate search to see if the word or phrase makes sense. The term or keyword may seem familiar, but if the spelling is off, it might not be worth anything. Even if the spelling makes sense and the word or term means something, it might be uncommonly used, leaving it with little commercial value. A general Google search with the word or a quoted search for the phrase can generally show me whether this is a popular term or not.
One of the best ways to tell if the keyword or term is popular or commonly used is to search for it in the most popular ccTLD(s) for the language. For instance, if the term is Spanish, I like to search for the .mx, .es, and .co domain names to see if they are registered and how they are used. If the keyword or phrase ccTLDs are being used, there is a decent chance the matching .com domain name will have value. There are other searches that can be done using Google and DomainTools to see if the keyword or phrase are registered and being used in longer tail ccTLD domain names, but these might be less effective because a longer tail domain name with a particular keyword might make a totally new word or term if it is combined with another word.
I tend to stay away from non-English domain names because of my poor language skills. Not only is it more difficult for me to determine commercial potential, but I also understand that people who are interested in the domain name may not speak English when trying to buy the domain name. This could make it more challenging to sell! That said, I would not want to pass up the opportunity to buy a great non-English .com domain name.