From Bulbapedia, the community-driven Pokémon encyclopedia.
While when nicknaming a Pokémon, the censored word must match the nickname exactly (ignoring case). However, when trading Pokémon over the GTS, if a Pokémon's nickname even contains a censored word, it cannot be traded. Due to this, there are some Pokémon who cannot be traded without nicknames due to their names containing a censored phrase. Even if a Pokémon may be banned for multiple reasons, only one reason is noted.
List of Pokémon that cannot be traded in certain languages