Set UTF-8 as default for Ruby 1.9.3

I'm on Rails 4 and Ruby 1.9.3

I use "strange" characters very often, so I have to declare UTF-8 encoding at the top of all .rb files.

Is there any way to set UTF-8 as the default encoding for Ruby 1.9.3?

I tried all answers, but when running rake db:seed and creating an object whose attributes contain non US-ASCII valid characters, I still receive this error:

`block in trace_on': invalid byte sequence in US-ASCII (ArgumentError)