English in phonology alone, without English grammar or lexicon: PRISENCOLINENSINAINCIUSOL
English with standard grammar but nonstandard phonology and some nonsense lexicon: THE FRIM-FRAM SAUCE
English in the academic register (with standard phonology and grammar; non-colloquial lexicon): Conversation on Husserl and Heidegger
Increasing divergence from Standard (phonology, grammar, lexicon) in three versions of a Jamaican story
Languages can be divided one from another by extreme divergences in all three features, to the point of mutual incomprehensibility.
Dialects are to some degree mutually comprehensible by speakers of the language to which they belong, but show marked differences in terms of the three features. Dialects are associated with regions, and sometimes too (where segregation exists) with ethnicities or other "marked" groups (such as religions) within a region.
Registers show more minor differences in grammar (often in terms of usage) and phonology, but often marked differences in lexicon and in the pragmatics of how conversations are conducted. Registers are associated with social class, but also with such factors as ethnicity, age, gender, and subject-matter contexts, especially where those intersect with class, as most famously studied by William Labov.
Jargons differ mostly in lexicon, and are associated with occupations or interests – which may also sometimes strongly align with class and gender and age, or with ethnicity, as those other factors line up with occupation and interest.
Moving from one language, dialect, register, or jargon to another is called code-switching: rare is the speaker who never switches codes.
Can one really talk about the same thing in different languages, dialects, and registers? Is reality changed for us by the ways we talk about it? Some stray examples:
frequency of mention studies