Modding Wiki's
For Russian-speaking users, there exist a GTAModding Wiki, it's quite similar to the normal GTAModding Wiki, but better because it's in Russian, and even has its own forum!
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For Japanese-speaking users, there exist a Wiki also, (this Wiki is mainly for CLEO3) if you can speak Japanese then you may want to check it out.
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For American's (or other English-speaking users) as you know the best Wiki for you is the GTAModding Wiki, all is in English, and is updated quite regally.
GTA Modding Forums
GTAMaps.net is a forum for Russian-speaking users, not only this, - but also general forums such as computer help, and etc.
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GTAForums.com is a very-large website for the Grand Theft Auto community, this is a American site, thus, the language is English (American-English).
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GTA-Action.com is a German speaking site, and forum. The website is consistently large, although not quite as massive as GTAForums, for English-speaking users (who can not understand the German language), there is a English option, but it's better without it.
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GTAForum.nl is a Dutch-speaking website, this website is the main forum for Dutch-speaking users, its design is similar to that of the Grand Theft Auto Wiki, PartickW and others run it. Its most famous MOD's are/is Design Your Own Mission, and the up-coming MOD - The Green Light District (Modification).
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Forums.ag.ru (or known also as just AGFC), is a huge-forum for Russian-speaking users, it has tones of forums for all different games, partially a huge GTA forum for all the GTA games.
P.S. Most forums are in Russian