fixed pr780, uploaded LanguageCommand.java (#782)

* Fix the following issues:
1. HashMap non-thread-safe issus
2. Fix the same problem in pr621, but use a better implementation

Add the following functions:
1. There is now a language cache inside getLanguage to prepare for different languages corresponding to different time zones where the accounts in the server are located

* add /language command,each account has their own Locate

* I forgot to git add...sorry,,this pr is to fix pr780, uploaded LanguageCommand.java