What's the difference between "lingo" and "jargon"?

Lingo is another word for jargon, but also a slang term for human language as well (at least in BE).

We visited Spain but didn't speak the lingo.

This example uses "lingo" to mean "language".

Working in J2EE is simple once you understand the lingo.

This example uses "lingo" to mean "jargon".

I’d use lingo to characterize a style of speaking, characterized by words both newly-minted and appropriated for a specific meaning. For example, using drag to mean boring or tedious, bread to mean money, or man as a form of address all contribute to the lingo of counterculture in the 60s.

Jargon refers to a technical vocabulary that is shorthand for complex or elaborate concepts and practices. In technology, for example, it’s often characterized by acronyms and other terms coined by inventors and innovators. In law, medical practice, and academic research, it’s a combination of terms and concepts owed to history that are often anchored to their language of origin.

Lingo is simply a language or dialect used by a specific group of people.

Jargon implies that the language is limited to a specific profession or other group and that others find it difficult to undersand.

For starters, lingo has racist and colonialist overtones, unlike jargon. Lingo is informal, unlike jargon. Basically, never use it unless you want to convey that you care nothing for the socially appropriate use of language, and possibly offend any speakers of the mode of speech you are labelling as "lingo".