How double quotes are added in LC_COLLATE?

Question

On Centos 6.5, running locale produces:

LANG=en_US.UTF-8
LC_CTYPE=en_US.UTF-8
LC_NUMERIC=zh_CN.UTF-8
LC_TIME=zh_CN.UTF-8
LC_COLLATE="en_US.UTF-8"
LC_MONETARY=zh_CN.UTF-8
LC_MESSAGES="en_US.UTF-8"
LC_PAPER=zh_CN.UTF-8
LC_NAME=zh_CN.UTF-8
LC_ADDRESS=zh_CN.UTF-8
LC_TELEPHONE=zh_CN.UTF-8
LC_MEASUREMENT=zh_CN.UTF-8
LC_IDENTIFICATION=zh_CN.UTF-8
LC_ALL=

After running export LC_COLLATE="en_US.UTF-8", running locale produces: LANG=en_US.UTF-8 LC_CTYPE=en_US.UTF-8 LC_NUMERIC=zh_CN.UTF-8 LC_TIME=zh_CN.UTF-8 LC_COLLATE=en_US.UTF-8 LC_MONETARY=zh_CN.UTF-8 LC_MESSAGES="en_US.UTF-8" LC_PAPER=zh_CN.UTF-8 LC_NAME=zh_CN.UTF-8 LC_ADDRESS=zh_CN.UTF-8 LC_TELEPHONE=zh_CN.UTF-8 LC_MEASUREMENT=zh_CN.UTF-8 LC_IDENTIFICATION=zh_CN.UTF-8 LC_ALL=

LC_COLLATE="en_US.UTF-8" becomes LC_COLLATE=en_US.UTF-8. Double quotes are lost. How LC_COLLATE is set to "en_US.UTF-8"? If I run export LC_COLLATE='"en_US.UTF-8"', there is the following error:

-bash: warning: setlocale: LC_COLLATE: cannot change locale ("en_US.UTF-8"): No such file or directory
-bash: warning: setlocale: LC_COLLATE: cannot change locale ("en_US.UTF-8")

How I can set LC_COLLATE to "en_US.UTF-8" using some commands?