The diphthong change is the main characteristics of Okayama accent.
Such a change doesn't take place with all diphthongs.

abbreviation; Okayama accent (OA), Standard Japanese (SJ)

Example follows;

(1) letters -ai change to -ee.
vegitable --> yasai(SJ) --> yasee(OA)
guy --> aitsu(SJ) --> eetsu(OA)

(2) letters -ui chage to -ii.
bad --> warui(SJ) --> warii(OA)

(3) letters -ei change to -ee.
kind --> teinei(SJ) --> teeNee(OA)

(4) letters -oi change to -ee.
good --> yoi(SJ) --> yee(OA)

(4) letters -au change to -ou.
buy --> kau(SJ) --> kou(OA)

(5) letters -iu change to -yuu
say --> iu(SJ) --> yuu(OA)

(6) letters -ou change to -oo
cleaning --> souji(SJ) --> sooji(OA)

(7) letters -ae change to -ee.
frog --> kaeru(SJ) --> keeru(OA)

Pronoun of Okayama dialect.

1. I --> washi (for man), uti (for woman) --> watashi (for both man and woman in SJ)

2. you --> omee (for man), antaa (for woman) --> anata (for both man and woman in SJ)

3. he, she --> eetu (for man), anoko (for woman) --> kare (for man in SJ), kanojyo (for woman in SJ)

1. we --> washiraa (for man), utiraa (for woman) -->watashitati (for both man and woman in SJ)

2. you(pl.) --> omeeraa (for man), antaraa (for woman)-->anatatati (for both man and woman in SJ)

3. they --> eeturaa (for man), anokoraa (for woman)-->karera (for man in SJ), kanojyora (for woman in SJ)