Hi Oto,
in this case, I have to disagree with Jon a bit: It's true JMDL was promoted in a time of MicroStation/J, but as visible from your previous question, it still existed in V8 2004 Edition. True is that it was deprecated in 8.0, but it was available until V8 XM Edition release, when it was removed completely.
Any pseudocode (Java, NET...) can be decompiled back to "human readable code", usually not fully and never back to original source code form. I have not tried to decompile Java bytecode, but there are more decompilers available (like this one or even cloud based). I guess it's not important that it's "Bentley Java", because bytecode should be the same. But you will probably have to consult JMDL documentation to check JMDL API classes functionality.
With regards,
Jan