"Eternal Sunshine of the Spotless Mind" is taken from the poem Eloisa to Abelard byAlexander Pope.
How happy is the blameless vestal's lot!
The world forgetting, by the world forgot.
Eternal sunshine of the spotless mind!
Each pray'r accepted, and each wish resign'd;
Since the movie title is so long, the corresponding Japanese and Korean titles are abbreviated to only "Eternal Sunshine" written in katakana and hangul respectively.
Korea: 이터널 선샤인
Thailand: ลบเธอ...ให้ไม่ลืม = "Forget... to remember". A more literal translation is "Erase her... so as not to forget"
- ลบ = erase
- เธอ = second person pronoun signifying both male and female, third person pronoun signifying female
- ให้ = 1. so that..., for 2.give, grant 3.allow, consent (1st meaning in this case)
- ไม่ = no, not
- ลืม = forget
I guess the Thai tile is a bit spoiler-ish? :P