They do sound pretty similar. However, if you listen to people's inflexion when saying "det" vs "dig", I noticed that "det" is almost two syllables (day-ah), and people's voice generally go up when they say it. "Dig" seems to go down at the end, and just be one syllable (day). I know I'm a year late, but I hope this helps !
Thou is modern English. Early Modern English to be exact, but it's still modern English. Everybody's heard it, it's still a part of fixed phrases in ceremonial language, and it's part of Shakespeare. It's even used on occasion in Tolkien's work, which is modern English.
What's more, it's easier for a learner to learn the difference between du, dig, ni, er, man and en when told that all of these have exact equivalents in English, rather than teaching them all as 'you'.
No, it's Modern English but it's not modern English.
Please consider that tens if not hundreds of thousands of learners take this course to simultaneously improve their English. I don't want to teach them that people use "thee" and "thou" in standard modern English.
I can't reply to your other post for some reason, so I'll reply here.
My original point was that translations of du and dig into thou and thee should be accepted, because that's exactly what they are. Nobody's advocating teaching learners of English to say thou and thee, but rather to aid learners of Swedish in understanding the difference between du and ni.
I understand why you want those translations, but adding them absolutely would teach people the wrong idea. The system has a tendency to show any accepted translation, or even ask users to translate them back into Swedish. Surely you understand why I don't people to be asked to translate "I love thee" into Swedish.
This goes for native and foreign speakers both. Most native speakers think that thou and thee are formal forms. If I add them, a lot of people will inevitably learn that du and dig are formal forms in Swedish, despite the incorrect premise.
There are many old words that could be added to the course but which would only benefit a very tiny minority of our users, while confusing a much larger portion. Frankly, I don't wish to spend my spare time adding archaic language that would impact the course negatively when the concept of du / dig / ni / er isn't very complicated to begin with.