Pronouns become meesa and yousa, th sounds flatten to d, and sentences sometimes pick up an okeeday on the way out.
Gungan basic is built from a handful of consistent substitutions rather than random mangling. Pronouns take an -sa ending: I becomes meesa, you becomes yousa, we becomes wesa. The th sound flattens to d, so the becomes da and this becomes dis, a real feature of several English dialects, called th-stopping, which is what makes it recognisable rather than nonsensical. Adjectives pick up an -sa ending too. The pattern is consistent enough that you can extend it to new words yourself and the result still reads correctly.
Okeeday is added to roughly one sentence in three rather than to every one. That matters because an interjection appended to every sentence stops reading as speech and starts reading as a template, and the character's verbal tics are noticeable precisely because they are intermittent. The same reasoning applies to the whole dialect: it works as a light consistent layer over ordinary sentences. Capitalisation is preserved through the substitutions, so a sentence that started with a capital still does after its pronoun has been replaced.
Because an interjection on every sentence reads as a template rather than as speech. Roughly one in three keeps it noticeable.
Yes. Pronouns take an -sa ending and th flattens to d, which is a real dialect feature called th-stopping. You can extend the pattern yourself.
Only the trailing interjection is random. The word substitutions are deterministic and give the same result every time.