[torstenvl]

> no alveolar consonants at all in the Slavic languages

That is a very strong claim... It's only true if you squint at it just right. You'd have to consider velars not to be consonants, since all Slavic languages have [n] to my knowledge, or perhaps give undue weight to a language's allophones (which tend not to be semantically meaningful). And you'd have to consider "alveolar" to mean only "strictly alveolar in the standard dialect," excluding consonants that are palatal-alveolar or post-alveolar in the standard dialect and making no allowance for regional accents or idiolects.