Write in English with altered rules; for example,

a) Spell based on phonetics; “Yesterday I red the noozepaper”.
b)Use irregular verbs in a regular manner; “I thinked for myself that beed quite unpleasant”
c) Use Newspeak; “Ungood” rather than Bad.
d)Use regulars in an irregular manner: “After I visat them I thunk the family for their attentions”
e)Alter the grammatical order (Subject-Verb-Complement); “We in the park met” (SCV)
f)Write like a non-native speaker would: “Visit us a person from the stranger country”

Difficulty; it must be justified within the story, don’t just alter the grammar and spelling of an existing one.