The Rosetta Stone
The Rosetta Stone is an ancient artifact, a stone weighing over 3/4ths of a ton, on which is carved the same passage in three different languages. At the time of its discovery, only one of the three languages was known to scholars. However, once someone realized that the three passages were supposed to cover the same text, each in its own language, this was the key to deciphering the two untranslated languages.
This term has migrated to the programming world with sites like RosettaCode where the same problem is solved in many different languages. In theory, a Python programmer could learn J by finding a number of problems on that site with examples in both languages and compare them to understand how one translates to the other. However, as someone once said, "In theory, theory and practice are the same but in practice they're not." While that method may have merit for someone who already understands some things about J, a bit more guidance is better for most beginners.
We need to have curated lists of translations, something like the following.
J equivalents of a few common Excel expressions with a listing of a great many Excel primitives.
Some comparisons between J and Python expressions.