Multi language domains

since domains per language can be set i have been wondering what the best practice is.

while most likely what i read people talk about

en.domain.com
de.domain.com
fr.domain.com

or on the other hand
domain.com/en
domain.com/de
domain.com/fr

which both work basically the same as in terms of seo and geo identification.

how about using translated domains instead? i assume this should be possible by language settings but is it a good idea or should this rather be avoided?

e.g.

buykirby.com
kaufkirby.com
acheterkirby.com

(or even with respective geo domain ending (.de, .com, fr)…