It falls in a very broad area. Like many examples of slightly outdated English, we understand it effortlessly, it doesn't sound strange, but we would be unlikely to say it in everyday speech today.
Of course, it is hard to imagine expressing such a line of high drama using everyday speech. It is hard to make a small change that will make it sound "modern," because using the word "tongue" to mean "the thing we speak with" also falls in the category of "things we understand but rarely say." The first things that come to mind are:
"Murder always speaks, even though it has no mouth."
"Murder, despite having no mouth, will speak."
Of course, we could say
"Murder, though it has no tongue, will speak."
The phrase "It might have been..." sounds completely natural to me; unfortunately, I'm not sure whether or not that is an example of the subjunctive!
P.S. I'm learning Spanish myself. Unfortunately, using the English subjunctive to explain the Spanish subjunctive is useless, because it is rare in English; when we do use it, we do it intuitively and do not notice what we are doing; and it is hardly ever mentioned in school.