What else would they use?

Of course they could pronounce the words in any modern Chinese language, but why not pick the largest and most standardized one?

For starters, a Chinese language which preserves final stops (-p, -t, -k) would be a better choice (e.g. Cantonese). These disappear completely in Mandarin, leaving rhymes (the vowel + final consonant) underspecified or ambiguous in many cases.