gmodjp_0.9.zip

This download looks like an addon. You need to extract the downloaded zip and put the addon folder in your Garry's Mod addons folder. You should end up with a directory structure similar to below:

• steamapps
  • common
    • garrysmod
      • garrysmod
        • addons
          • gmodjp_0.9 <-- Addon folder!
            • e.g.
            • lua
            • maps
            • materials
            • models
            • etc

• gmodjp_0.9/
  • resource/
    • fonts/
      • akbar.ttf
      • akbar.txt
      • coolvetica.ttf
      • coolvetica.txt
      • csd.ttf
      • csd.txt
      • readme.txt
      • TF2.ttf
      • TF2Build.ttf
      • TF2Professor.ttf
      • TF2secondary.ttf
    • game.ico
    • gameui_japanese.txt
    • garrysmod_japanese.txt
    • HL2MP.ttf
    • language/
      • constraints_japanese.txt
      • construction_japanese.txt
      • faceposer_japanese.txt
      • main_japanese.txt
      • materials_japanese.txt
      • misc_japanese.txt
      • models_japanese.txt
      • npc_ents_english.txt
      • poser_japanese.txt
      • postprocessing_japanese.txt
      • render_japanese.txt
      • sandbox_cleanup_japanese.txt
      • sandbox_hints_japanese.txt
      • sandbox_settings_japanese.txt
      • sandbox_undo_japanese.txt
      • server_setup_japanese.txt
      • settings_japanese.txt
      • wheels_japanese.txt
  • âèü[âhâ~ü[.txt

anenisk, 鉄棒ぬらぬら, あい, yokoiatsushi252, Colttyy, KingPanda164, pueru_game, masao1012group, RobinHood3648, madao2800, rin.ren.master, yukihiro0309, SCP-040-JP, norazero-4137, ancogame110, risakooooo_M, tokiya1024, Tousei_Kiritan(10th.), カフェオレさん, くさや, Quatri, frisk （JP）, kikoushiryu, keisukehanyuda, tenshihakokoni, ikeshun1031, dotekabocha, vividra, karpato0614, SIROCRAFT19, miya2438, しき, ren2089, hipuno, kmt_skb, arigasora, kurt_ney, hayasaka_saika, 0ct09927729172t, ramumaru, isofurabe, 借り暮らしのナナ, syk, nakatatsu1225, FantasyLife, qwert70, 711hibiki711, kth27045, saika_0310, Hikikomori-Youjo +1942 others