ובדבר אם מותר לאכול ברעסטאראנט שמכינים שם רק מאכלי חלב אבל הם של אנשים מחללי שבת, הנה אף שם אפשר להיות כמה מאכלות אסורות כדגים טמאים, וגם השומן שמטגנים בהם אפשר שהם מבהמות אפודות ונבלות, וגם גבינות אסורות, ויש גם דברים שאסורים משום בשולי עכו״ם, ולכן אף ליכנס לשם לאכול דברים הידועים שאין בהם שום חשש איסור יש לאסור מפני מראית עין וחשד.
I'm trying to understand this, but I don't fully understand the Hebrew. Is there an English translation out there somewhere? If not, can you please translate the whole paragraph for me?
And as for the matter of whether it's permissible to eat in a restaurant in which they prepare only dairy foods but which is of people who desecrate the sabbath, lo, even in that place there can be a number of forbidden foods such as non-kosher fishes, and the fat in which they fry [things] can be from non-kosher animals or animals not properly slaughtered, and [there may be] forbidden cheeses, and there will be things forbidden as having been cooked by a non-Jew. Thus, one should forbid even entering there to eat things that are known to lack even a suspicion of prohibition, because of mar'is ayin [=others' seeing it] and suspicion [of the one entering]. But if he's exceedingly hungry, that he's in a great deal of discomfort, and there's nowhere else to eat in that area, he can enter there to eat things known [to be] permitted, but this must be secretly: for in a case of pain and loss the rabbis did not decree, as is [noted] in K'suvos daf 60. That is, outside [the restaurant] should not be people who recognize him: for before the people inside, well, they'll see he's taking only things known [to be] permitted. If people who recognize him are there, outside, he must tell them he's in a great deal of discomfort so is entering there to take something known [to be] permitted. But without his being in a great deal of discomfort, he should not enter there at all.
Do not trust my translation for halachic purposes! Consult your rabbi.
Here is my heavily-copyedited version of the translation that msh210 did. I also thank b a and R' Tzvi Hirsch Haber; their translation work helped me too. All errors in this version are mine, not theirs.
Are you allowed to eat in a dairy restaurant run by non-Sabbath-observers? Even here, there may be non-kosher foods. For example, certain fats, cheeses, and kinds of fish; plus foods forbidden because they were cooked by non-Jews. Don't go in even to eat definitely-kosher food, due to [a prohibition called] maris ayin and [a different prohibition called] chashad. But if you're exceedingly hungry, i.e. in a lot of discomfort, and there's nowhere else to eat in the area, you can go in to eat definitely-kosher food. This is because the rabbis didn't enact their edicts in a case of pain or loss (tractate Kesubos 60). But you must do so secretly. Nobody outside the restaurant should recognize you. (The people inside will see that you're only eating kosher.) If people who recognize you are outside, you must tell them that, because you're in a lot of discomfort, you're going in to eat kosher food. But if you're not in a lot of discomfort, don't go in at all.
There are other cases where there may be no problem whatsoever to enter the venue. These may include many cafeterias (see the relevant articles by R' Yirmiyohu Kaganoff and R' Eli Gersten) and certain business meetings in non-kosher restaurants.
Do not trust this translation for halachic purposes.