I haven't formally defined the supported subset. The 16 test cases, especially coverage.py should give you a sense.
JavaScript is possible via python to dart to JavaScript.
Adding another backend is easy, given there are 7 backends already.
Are dicts ordered? Not by default. It should be possible to translate Python's ordereddict to one in the target language.
Just mapping max/min was hard enough. In some languages max(1,2) produces a float!