>The spanish version(s) would be:
>
>"A caballo regalado no se le miran los dientes" or
>"A caballo regalado, no hay que mirarle el diente" or
>"A caballo regalado, no le mires el dentado"
>
>The first one is the one I knew, the other two I just googled, the third one rhymes nicely
>
>in case you want to start a collection <g>

OK, adding:
"Poklonjenom konju ne gledaj u zube"
"Поклоњеном коњу не гледај у зубе" (the same, just in Cyrillic). And this could have been worded in several other ways (pretty much just like the examples you provided), but this 12-syllable version is the one that stuck. Probably because of the exact Alexandrine rhythm - and now that I've thought about it, most of our proverbs fit into either that, or 8-syllable or (the preferred epic format) a decameter.

>>"Darenomu kon'ju v zuby ne smotrjat".