Listened to your link ---
Sample and reverse - play backwards - which is how the example samples seem to have been doctored in at least one case.
The other technique that has been used here is to split off individual notes, some with a phoneme (or recognizable consonant at the beginning of the ample), others without (vowel only - ah-eh-ih-uh) then making it into a multi-sampled "construction kit" - in this case only a bit over an octave.
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Three things I heard...
One - same person used for all samples -- probably same record too -- makes for a much more consistent result.
Two - Not foreign, just out of context -- sample pieces of words - in a given recording (even a short one) many words are available - mix 'em up til they make no sense... the "foreign-ness" is a case of hearing the sounds out of order...
tpantano = ta-ta-no-a-a-o-o-a-pa-<apt-no-no
[you can see how that might result in something independent of language context]
Three - minimal pitch changing -- only on the highest notes was there a noticed change in vibrato due to re-pitching the sample. The more range to the original sample notes, the more natural they will sound in the kit.
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A place you might start is ambient vocals - Celtic stuff - Enya, Clannad... any place where a vocal over a pad is part of the norm -- a lot of the Irish ladies have distinctive (good!) vocals and the range you're looking for.
BB