I want to put crafting speed in half time. What exactly do I need to change here:
crafting.timescale "0.1"   - This is how it is set by default. What I need to change is to reduce my crafting speed by half ?

in your config

"Default crafting rate percentage": 50.0,​

50% is equivalent to half the normal speed.

It looks like you may be using an old version of the plugin since there is no longer a crafting.timescale option.

I do not use any plugin. 
crafting.timescale "0.1"  it stands inside my config file. Is it possible to set this in my config file?

not sure why you are posting about your server cfg pm this plugin support page.

you could try crafting.timescale "0.5"

or just use this plugin to manage craft time,