I've utilized Monolingual with caution for some time now and it has always performed flawlessly. it is important however, that one read the notes and fully understand the power of this tool. That said however, this newer version appears to be unstable with 10.3.9, despite the developer's claim to the contrary. Sometimes it launches, other times it crashes with a thud, at least for me. Otherwise, it's a very useful tool, though dangerous in the hands of those who blindly unleash it's power.