Board Game Arena

http://wordlist.aspell.net/12dicts-readme/

I guess it uses 3of6game (International) ?

It's a bit harsh as it removes all words starting with a capital letter including words like February or Easter.

It is a combination of 2of12inf + 3of6game. I chose these because they have inflections (all forms of the word, for example: cheese, cheeses, cheesier, cheesiest, cheesiness, cheesy) and because they already filtered out words not acceptable in most word games -- like acronyms/initialism (FBI, USA), hyphenated words (tractor-trailer), phrases, and proper nouns. Generally, these categories aren't allowed in other games like Scrabble, either.

This means you shouldn't find cities, days of the week, months of the year, zodiac signs, etc. in any of the lists. This is true for 12dicts, but the Scrabble dictionaries are very inconsistent. For example, British Scrabble does not contain Aquarius, Christmas, February, London, but does contain Gemini, Easter, November, Berlin.