Re: how to find and replace text in frontend side via plugin?
You could try GlotPress:
http://blog.glotpress.com – GlotPress blog
It’s not a plugin, but it allows you to translate scripts using a front-end interface.
There’s not much documentation or anything like that since it’s still quite an early script, but if you feel the need to edit language files using a front-end script, GlotPress is an option.
Just found the following WordPress plugin:
It’s a little old, but you could give that a shot as well.