I translated some well-regarded public domain works into English. I make around 2-3k a month from the ebook sales. If you find niche areas of interest or research it can be quite lucrative. Of course you invest the time to translate but I find it rewarding and less like actual "work"
I often have specific authors or periods in mind - such as when I am reading a book and come across a reference to an untranslated author or piece - and so I just search for the source text (usually on wikisource or gutenberg) and make sure its public domain.
I publish them myself, yes - there is a "press" I put them under but its just me. I have a few friends who do reviews and I am also on several academic mailing lists
I'd prefer to stay anonymous on this site but I will say there are a lot of French horror /occult stories from the 19th Century that are in the public domain and attract a niche following. For instance, one of the seminal works of demonology, "Dictionnaire Infernal", remains largely untranslated into English.
