PokéWiki – Die deutsche Pokémon-Enzyklopädie is an alternative as well. I’ve used a combination of BisaFans and PokeWiki when I made my German ‘Pikachu around the World’ collection post, mostly for the release dates of sets/promos.
I tried to use similar wikis for information of the other languages, so I’m just gonna post them here for completeness in case anyone else is looking for release information in a specific language:
- English/Japanese (added for completeness): Pokémon Trading Card Game - Bulbapedia, the community-driven Pokémon encyclopedia
- Dutch: In my youth, I used to use pokemon-paradijs.com a lot, but that website is offline for years now, so you’ll have to use a web archive variant: https://web.archive.org/web/20200627154206/http://www.pokemon-paradijs.com/ruilkaarten/ruilkaarten.php (doesn’t contain Dutch release dates, though - although I know the Dutch Base Set was released on February 25th, 2000).
- German: the earlier mentioned PokéWiki – Die deutsche Pokémon-Enzyklopädie and Bisafans.de — Pokémon von Fans für Fans!
- French: https://www.pokepedia.fr/
- Italian: https://wiki.pokemoncentral.it/
- Spanish: WikiDex, la enciclopedia Pokémon
- Portuguese: https://www.ligapokemon.com.br/, and this recent thread using Copag’s different sources with Web Archive might possibly help as well: How to Research Copag (Portuguese) Cards
- Korean: Partially Bulbapedia up to about 2011: Start of an Adventure (KTCG) - Bulbapedia, the community-driven Pokémon encyclopedia, after that 포켓몬 카드 게임
- Traditional Chinese: not sure about the Base Set and EX Legend Maker set, but from 2019 onward you can use Bulbapedia: All Stars Collection (ATCG) - Bulbapedia, the community-driven Pokémon encyclopedia (search for ATCG or TCTCG)
- Polish: none that I could find, but the two sets are released on January 12th, 2010 (Diamond & Pearl) and June 1st, 2012 (Mysterious Treasures) respectively, and apart from the Pikachu World Collection 2010 there aren’t any Polish promos or holo/stamped variants.
- Russian: incomplete and partially broken wiki, but for the first two sets I’ve used https://pokeru.shoutwiki.com/wiki/, and for later sets a Russian user helped me at the time
- Thai: Bulbapedia First Impact (ATCG) - Bulbapedia, the community-driven Pokémon encyclopedia (search for ATCG or TTCG)
- Indonesian: Bulbapedia: First Impact (ATCG) - Bulbapedia, the community-driven Pokémon encyclopedia (search for ATCG or ITCG)
- Simplified Chinese: Card Lists - Simplified Chinese / Indonesian / Japanese / Korean / Thai Pokemon cards | KrystalKollectz (in the past I used to use a combination of Bulbapedia (ATCG/SCTCG) and 太阳&月亮系列（TCG） - 神奇宝贝百科，关于宝可梦的百科全书)
- Latin American Spanish: no idea, haven’t looked into them yet
Greetz,
Quuador