Java Script project localisation

I need a Java script developer who will upgrade existing project (about 500 lines of code) that all screen strings will be read from the local txt file instead to be hardcoded on the file. Txt file will be used also for all project constants. Every string in the file will have the name, so the position of the string in the file will not be important.

External file will be used for translations and project should run under UTF-8 to show also different alfabets.