www.pokebeach.com/forums/thread-foreign-cards-database-in-the-works-updated
www.copag.com.br/pokemon/colecao-xy/
www.elitefourum.com/t/pokemon-card-language-library/13032/1
wiki.pokemoncentral.it/
www.playon.de/
es.pokemon.wikia.com/wiki/Lista_de_expansiones_del_Pok%C3%A9mon_Trading_Card_Game
pokeru.shoutwiki.com/wiki/%D0%97%D0%B0%D0%B3%D0%BB%D0%B0%D0%B2%D0%BD%D0%B0%D1%8F_%D1%81%D1%82%D1%80%D0%B0%D0%BD%D0%B8%D1%86%D0%B0
In additional to things like eBay from various countries, multiple online stores for various countries (like ultrajeux.com, frikea.es, pokemoncardmarket.eu, cardgame-club.it, collect-it.de, lotticards.de), and various countries’ Facebook groups (and the folks that live in said countries).
That’s been basically what has kept me up on Pikachu’s as well. Having contacts in various regions has been an incredible asset that I think would be essential to having a complete database for something like this.