I tried to search it before but my English is not good and I couldn't find nothing. You don't have to be rude. Don't help if you don't want to. And thanks for information.
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Euroaion Client doesn't have esp.pak and l10n folders are differents than the tutorial you sent.
- Aion l10n folders:

- Euroaion folders: (they haven't any FRA.pak, ITA.pak, ESP.pak, etc)

Even, bat. lines are different.
My lines are: start bin32\\aion.bin -ip:127.0.0.1 -port:2106 -cc:2 -lang:enu -noweb -nokicks -ncg -noauthgg -ls -charnamemenu -nowebshop -ingameshop -win10-mouse -win10-mouse-fix-autodetect
I can't write the same lines of the tutorial because it doesn't exist "L10n/ESP/ESP.pak"
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I could change the Language without using Euroaion Client. That post gave me the clue, but I had new problems because it isn't the same Game version. (Euroaion and My 4.6 Aion don't match).