There have been several claims for the 'longest sentence in the English language' revolving around the longest printed sentence.
Sentences can be made arbitrarily long in various ways.
One method is successive iterations, such as "Someone thinks that someone thinks that someone thinks that nobody thinks that...,"[1] while another method is combining shorter clauses.
Sentences can also be extended by recursively embedding clauses one into another, such as[2][3] This also highlights the difference between linguistic performance and linguistic competence, because the language can support more variation than can reasonably be created or recorded.
[1] As a result, one linguistics textbook concludes that, in theory, "there is no longest English sentence.