This is an interesting idea but awkward to use. I am semi-literate in Chinese so I selected intermediate Chinese immersion. I like that the words can be reverted to the original language, but having these Chinese words littered amongst a sea of English words is odd and difficult to process. If you go through an article and you're met with a Chinese word, your brain can't immediately process the new language. The constant switching between languages when it comes to reading is quite cumbersome, even if it is for the sake of learning. This is particularly so for languages of different forms like English and Chinese. Words/phrases that are slang cannot be directly translatable, which is detrimental to beginners who do not know that it has been incorrectly translated. I think it is mildly useful for intermediate leaners trying to increase their vocabulary set but not for language immersion or introduction to a new language.
But would you need to use the tool if you could read an entire passage in that language? If you were literate in that language, you could just go to a native newspaper website and read those articles (something which I cannot do). And I think a mildly fluent person would find translated passages hard to read, which is why I don't translate Chinese websites into English (aka Engrish). The only advantage the language immersion plugin has is the ability to hover over the passage if you don't understand what it means, but it's annoying to do if you just don't understand an individual word/phrase and the whole passage gets reverted to the original language.
